Jostein Røyset - Academia.edu (original) (raw)

Papers by Jostein Røyset

Research paper thumbnail of Effects of scandium addition in wrought aluminium alloys

A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a consi... more A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a considerable part of the available literature on Scandium in Aluminium alloys. Paper 2 and Paper 3 is a study of isothermal precipitation kineetics and mechanisms in a binary Al-Sc slloy. Precipitaion of the equilibrium phase A13Sc was found to occur either continuously or disontinuously, depending on teh temperature. Measurements of electrical conductivity were used to estimate the solvus line of SC in A1, and for estimating the interface energy between A13Sc particles and the A1 matrix.Paper 4 and Paper 5 are studies of alloys in the ternary A1-Mg-Sc and A1-Sc-Si systems, respectively. It was found that Mg had no marked influence on the precipitaion behavior of A13Sc, and the A13Sc particles were found to prevent recrystallisation of a deformed A1-Mg-Sc alloy even when it was heated to temperatures close to the solidus. Si, however, was found to have a strong influence on the precipitation hardening potential of A1-Sc-Si alloys. At 500°C the A13Sc particles were found to disappear with increasing Si level.In Paper 6 and Paper 7 the effects of adding Sc and Zr to an A1-Mg-Si alloy are explored. A13Sc particles could be formed during heat treatments at 550°C when at least 0.2 wt.% Sc was added by to the slloy. However, the highest number density of particles was achieved by adding both 0.2 wt.%Sc and 0.1wt.%Zr to the alloy. The A13Sc particles did not act as nucleation sites for Mg2Si, and the Sc addition to the alloy did not have any influence on the preciptation hardening of the alloy. In hot rolled material, one did not manage to identify A13Sc particles. In specimens that were hot rolled material, solutionised and then age hardened, the ductility was found to increase with increasing Sc level, while 0.4wt.%Sc was found to decrease the strength of the alloy somewhat.

Research paper thumbnail of Scandium in aluminium alloys

International Materials Reviews, Feb 1, 2005

A considerable part of the available literature on scandium in aluminium alloys is reviewed. Expe... more A considerable part of the available literature on scandium in aluminium alloys is reviewed. Experimental data and assessments of the binary Al-Sc phase diagram, a wide range of ternary Al-Sc-X phase diagrams and a few higher order phase diagrams are accounted for, with emphasis on the aluminium rich part of the diagrams. The phase which is in equilibrium with Al, Al 3 Sc, can form by several different mechanisms, all of which are described. The precipitation kinetics of Al 3 Sc in binary Al-Sc alloys are discussed, and an overview of the reported influences of ternary alloying elements on the precipitation of Al 3 Sc is given. The Al 3 Sc phase particles can serve as a grain refiner in the Al melt, a dispersoid for controlling the grain structure of the alloy and a strengthening precipitate. Several examples of these three effects are mentioned, both in binary Al-Sc alloys, and in more complex alloys. The reported effects of Sc on the precipitation behaviour in Al-Cu, Al-Mg-Si, Al-Zn-Mg and Al-Li alloys are also revised. A brief account of the effects of Sc additions on the corrosion behaviour of Al and Al-alloys is given. Finally, some views on the current and future use of Sc-containing Al alloys are given.

Research paper thumbnail of Precipitation in Some Dilute Al-Ge-Si Alloys

International Journal of Materials Research, Nov 1, 1995

Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respec... more Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respect to solvus temperatures, solid solubility at 400 °C and precipitation behaviour at 160 °C. Solvus temperatures were determined both by measurements of electrical resistivity and by scanning electron microscopy (SEM). The results of the two methods were fairly consistent. Specimens annealed at 400 °C were studied by SEM. The area fractions of the precipitates were measured, and used for calculations of the solid solubility of the alloys at this temperature. From the results obtained, one has proposed a most likely shape of the isothermal sections of the Al-rich solvus surface. Age hardening experiments showed an improved hardness in some of the ternary alloys, as compared to the binaries. However, it seems like all alloys are equally dependent on the quenched-in vacancies to facilitate nucleation of precipitates.

Research paper thumbnail of Effect of Low Cu Addition and Thermo-Mechanical History on Precipitation in Al-Mg-Si Alloys

Materials Science Forum, Jun 1, 2014

The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformat... more The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformation on precipitation hardening in two Al-Mg-Si alloys is investigated by transmission electron microscopy (TEM), and related to material hardness. Two alloys have been used, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes. A double peak hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. The 1% pre-deformation also made this effect less pronounced, but it led to faster initial hardness evolution and delayed over-aging. Maximum hardness was not influenced by cooling rate and the pre-deformation. Hardness was directly related to precipitate number densities.

Research paper thumbnail of Scandium In Aluminium Alloys: Physical Metallurgy, Properties And Applications

Metallurgical Science and Tecnology, Sep 5, 2013

The use of scandium as an alloying element in aluminium has gained an increasing interest even th... more The use of scandium as an alloying element in aluminium has gained an increasing interest even though scandium is difficult to extract, which makes the metal very expensive. The three principle effects that can be obtained by adding scandium to aluminium alloys are (i)grain refinement during casting or welding, (ii)precipitation hardening from Al 3 Sc particles and (iii)grain structure control from Al 3 Sc dispersoids. Addition of scandium in combination with zirconium is particularly effective, and the reason for this is linked to the recently discovered core/shell structure of the Al 3 (Sc,Zr) dispersoids. The effects that can be obtained from a Sc addition are to a large extent dependent on the alloy system to which it is added, and an overview of some effects in all the major classes of wrought aluminium alloys is given. Industrial use of Sc-containing aluminium alloy is so far limited to a few aerospace applications and to sporting equipment, further use is dependent on a price reduction of scandium. AL-SC MASTER ALLOYS When adding alloying elements to an aluminium melt, this can be done either by adding the pure elements or by adding the elements in the form of master alloys. Adding pure Sc to the melt is technologically feasible. From the binary phase diagram in Figure 2 [11, 16] it is evident that unless the melt is heated to a temperature higher than approx. 1185°C a sequence of phase

Research paper thumbnail of Precipitation in Some Dilute Al-Ge-Si Alloys

International Journal of Materials Research, 1995

Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respec... more Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respect to solvus temperatures, solid solubility at 400 °C and precipitation behaviour at 160 °C. Solvus temperatures were determined both by measurements of electrical resistivity and by scanning electron microscopy (SEM). The results of the two methods were fairly consistent. Specimens annealed at 400 °C were studied by SEM. The area fractions of the precipitates were measured, and used for calculations of the solid solubility of the alloys at this temperature. From the results obtained, one has proposed a most likely shape of the isothermal sections of the Al-rich solvus surface. Age hardening experiments showed an improved hardness in some of the ternary alloys, as compared to the binaries. However, it seems like all alloys are equally dependent on the quenched-in vacancies to facilitate nucleation of precipitates.

Research paper thumbnail of Al-Mg-Si billets with high extrudability – state of the art and beyond

Materials Today: Proceedings, 2019

Within the alloy groups EN-AW6060 and EN-AW6063 a range of alloys termed "High Speed Alloys". hav... more Within the alloy groups EN-AW6060 and EN-AW6063 a range of alloys termed "High Speed Alloys". have been developed. The underlying metallurgical principles of this development are explained. Further, new technological developments and new experimental discoveries have led to a new, upcoming billet quality, "HP 6xxx". Three different billet qualities, "Standard 6060", "High Speed 6060" and "HP 6060" were compared in a full-scale industrial trial, and the results indicate that the improvement in extrudability of "HP 6060" over "High Speed 6060" is of the same order as the improvement of "High Speed 6060" over "Standard 6060".

Research paper thumbnail of The Effect of Elastic Strain and Small Plastic Deformation on Tensile Strength of a Lean Al–Mg–Si Alloy

Metals, 2019

Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusio... more Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusion, the aluminium profiles are usually straightened, causing the material to be subjected to a small plastic deformation. This study demonstrates the positive effect on strength that can be obtained from such small deformation levels or from only elastically straining the material. Elastic straining of a lean Al–Mg–Si alloy, when performed immediately after solution heat treatment, enhances the material yield strength after artificial ageing to T6. Transmission electron microscopy shows that this effect can be attributed to a higher number density and finer dispersion of the age-hardening precipitate needles. Furthermore, introducing a small plastic deformation of 1% after solution heat treatment results in a comparable strength increase to elastically straining the material. In this case, however, the strength increase is due to the increased dislocation density, which compensates for a ...

Research paper thumbnail of The effect of alloying elements on the ductility of Al-Mg-Si alloys

Materials Science and Engineering: A, 2017

Experiments were conducted to attempt to understand the effect of different alloying elements on ... more Experiments were conducted to attempt to understand the effect of different alloying elements on the ductility of Al-Mg-Si alloys. Four alloys with different concentrations of Si, Mg, Fe, Mn and Cu were selected for examination. The strength-ductility relationship was evaluated by tensile tests, and microscopic analysis in light optical microscope, SEM and TEM was conducted to investigate grain-, constituent-, precipitatation-and fracture characteristics. Excess-Si (Mg/Si>1.73) was found to have a detrimental effect on the ductility of Al-Mg-Si alloys, without the presence of additional alloying elements. This alloy had an elongation to fracture of 23.1%, where failure occurred partly intergranularly, and was seemingly due to poor grain boundary characteristics. Adding Fe and Cu improved the ductility (and strength) to 42.9% elongation, and the change was related to the formation of secondary-phase particles, resulting in less free Si for embrittlement of grain boundaries. The best ductility, 79.2% elongation, was found by introducing Mn, which in addition to the above-mentioned changed

Research paper thumbnail of The effects and behaviour of Li and Cu alloying agents in lean Al-Mg-Si alloys

Journal of Alloys and Compounds, 2017

We show how replacing a fraction of Mg with Li in a lean Al-Mg-Si alloy gives comparable strength... more We show how replacing a fraction of Mg with Li in a lean Al-Mg-Si alloy gives comparable strength and enhanced temperature stability. Replacing solute with smaller amounts of Cu and Li also improves thermal stability and nearly compensates the strength loss for longer ageing times. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) documented Li and Cu causing modest structural changes to the main hardening precipitate, β". However, density functional theory calculations verified the observation from HAADF-STEM that Li preferentially occupies Mg3 sites in the β" structure.

Research paper thumbnail of The Effect of Heating Rate on the Density and Spatial Distribution of Dispersoids during Homogenisation of 6xxx Aluminium Alloys

Materials Science Forum, 2016

Two 6xxx alloys with different Mn-content have been homogenised in a furnace at 575 oC for 2 hour... more Two 6xxx alloys with different Mn-content have been homogenised in a furnace at 575 oC for 2 hours and 15 minutes. Three different heating rates to the homogenisation holding temperature were chosen, as this was expected to affect the precipitation behaviour of the dispersoids. The study focused on developing a reliable procedure for the characterization of the density and spatial distribution of dispersoids in aluminium alloys; both in terms of sample preparation, microscopic techniques and quantitative analyses of results. Scanning electron microscopy (SEM) has been used to evaluate the dispersoid characteristics for the different alloys and heating rates. The results indicate an increase in dispersoid number density and a more uniform distribution of dispersoids for the lowest heating rate, as compared to the more rapid heating rates, for the alloy with 0.05 wt% Mn. For the alloy with 0.15 wt% Mn the number density increased with the heating rate. This is suggested to be due to p...

Research paper thumbnail of Directionality and Column Arrangement Principles of Precipitates in Al-Mg-Si-(Cu) and Al-Mg-Cu Linked to Line Defect in Al

Materials Science Forum, 2016

In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that co... more In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that column surrounding of an element column in the needle/lath direction order according to simple principles. Advanced transmission electron microscopy and DFT calculations support the principles originate with a line defect, which is a segment of a <100>Al column shifted to interstitial positions. We propose the defect aids solute decomposition by partitioning the FCC matrix locally into columns of fewer and higher number of nearest neighbours, which suit smaller and larger size solute atoms, respectively. The defect explains how <100> directionality of the precipitates can arise in a cluster. Ordering of a few defects leads naturally to GPB zones in Al-Mg-Cu and to β'' in Al-Mg-Si.

Research paper thumbnail of Comparison of Properties of Extruded 6xxx Alloys in T5 Temper versus T6 Temper

In order to achieve the highest possible potential for age hardening in extruded profiles of 6xxx... more In order to achieve the highest possible potential for age hardening in extruded profiles of 6xxx alloys it is necessary to make sure that as much Mg and Si as possible is in solid solution before the ageing. This can be done either by a separate solution heat treatment, or by making sure that no (Mg,Si) particles are formed in the as-extruded profile prior to artificial ageing. The present paper explains how one can avoid (Mg,Si) particles in the asextruded profile, and the effect of billet preheating temperature is illustrated by an example from industrial scale experiments. Further, it is shown by examples from semi-industrial scale experiments with 6005 alloys that when precautions are taken to avoid (Mg,Si) particles in the as-extruded profile the T5 strength is at least as good as the T6 strength. In some cases a separate solution heat treatment may actually lead to a much lower strength in the T6 condition.

Research paper thumbnail of The Effect of Cu and Ge Additions on Strength and Precipitation in a lean 6xxx Aluminium Alloy

Journal of Physics: Conference Series, 2015

It has been demonstrated that the strength loss in a lean Al-Mg-Si alloy due to solute reduction ... more It has been demonstrated that the strength loss in a lean Al-Mg-Si alloy due to solute reduction could be compensated by back-adding a lower at % of Ge and Cu. Nanosized precipitate needles which are the main cause of strength in these alloys, and material hardness has been correlated to parameters quantified by TEM. It was found that additions of Ge and Cu strongly affect the precipitation process by increasing precipitate density and reducing precipitate size. Investigations of precipitate atomic structure by HAADF-STEM indicated that they contain mixed areas of known phases and disordered regions. A hexagonal Si/Ge-network was found to be present in all precipitate cross sections.

Research paper thumbnail of Effects of scandium addition in wrought aluminium alloys

A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a consi... more A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a considerable part of the available literature on Scandium in Aluminium alloys. Paper 2 and Paper 3 is a study of isothermal precipitation kineetics and mechanisms in a binary Al-Sc slloy. Precipitaion of the equilibrium phase A13Sc was found to occur either continuously or disontinuously, depending on teh temperature. Measurements of electrical conductivity were used to estimate the solvus line of SC in A1, and for estimating the interface energy between A13Sc particles and the A1 matrix.Paper 4 and Paper 5 are studies of alloys in the ternary A1-Mg-Sc and A1-Sc-Si systems, respectively. It was found that Mg had no marked influence on the precipitaion behavior of A13Sc, and the A13Sc particles were found to prevent recrystallisation of a deformed A1-Mg-Sc alloy even when it was heated to temperatures close to the solidus. Si, however, was found to have a strong influence on the precipitation hardening potential of A1-Sc-Si alloys. At 500°C the A13Sc particles were found to disappear with increasing Si level.In Paper 6 and Paper 7 the effects of adding Sc and Zr to an A1-Mg-Si alloy are explored. A13Sc particles could be formed during heat treatments at 550°C when at least 0.2 wt.% Sc was added by to the slloy. However, the highest number density of particles was achieved by adding both 0.2 wt.%Sc and 0.1wt.%Zr to the alloy. The A13Sc particles did not act as nucleation sites for Mg2Si, and the Sc addition to the alloy did not have any influence on the preciptation hardening of the alloy. In hot rolled material, one did not manage to identify A13Sc particles. In specimens that were hot rolled material, solutionised and then age hardened, the ductility was found to increase with increasing Sc level, while 0.4wt.%Sc was found to decrease the strength of the alloy somewhat.

Research paper thumbnail of Effects of Germanium, Copper, and Silver Substitutions on Hardness and Microstructure in Lean Al-Mg-Si Alloys

Metallurgical and Materials Transactions A, 2015

It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be comp... more It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be compensated by adding back smaller quantities of Ag, Ge and Cu. Nine alloys were investigated. Ge was found to be the most effective addition, strongly refining the precipitation. The hardness is discussed in terms of statistics of the precipitates near a T6 condition, as acquired by transmission electron microscopy. Precipitates in some conditions were also investigated by high angle annular dark field scanning transmission electron microscopy. The added elements have strong influence on the main hardening precipitate, '', changing its structure and promoting disorder.

Research paper thumbnail of Some comments on the misfit and coherency loss of AlSc particles in Al?Sc alloys

Scripta Materialia, 2005

An attempt of refining a recently reported calculation of the temperature dependent misfit betwee... more An attempt of refining a recently reported calculation of the temperature dependent misfit between Al and Al 3 Sc particles is given. Further, the impact of a temperature dependent misfit on the calculated diameter for coherency loss of Al 3 Sc precipitates is demonstrated. The origin of misfit dislocations is also briefly discussed.

Research paper thumbnail of Effects of Sn Addition on Microstructure, Extrudability, Mechanical Properties and Machinability of a 6082 Alloy

Materials Science Forum, 2002

Research paper thumbnail of Effect of Low Cu Addition and Thermo-Mechanical History on Precipitation in Al-Mg-Si Alloys

Materials Science Forum, 2014

The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformat... more The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformation on precipitation hardening in two Al-Mg-Si alloys is investigated by transmission electron microscopy (TEM), and related to material hardness. Two alloys have been used, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes. A double peak hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. The 1% pre-deformation also made this effect less pronounced, but it led to faster initial hardness evolution and delayed over-aging. Maximum hardness was not influenced by cooling rate and the pre-deformation. Hardness was directly related to precipitate number densities.

Research paper thumbnail of Influence of Low Cu Addition on Quench Sensitivity in Al-Mg-Si Alloys

Advanced Materials Research, 2014

Quench sensitivity in two Al-Mg-Si alloys, one Cu-free and the other with low Cu additions (~0.1 ... more Quench sensitivity in two Al-Mg-Si alloys, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes, has been investigated using transmission electron microscopy (TEM) and corresponding material hardness. A two stage hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. However maximum hardness was not influenced by cooling rate, which could be related to higher precipitate number densities and volume fractions. Both alloys were over-aged faster in the slow cooling conditions.

Research paper thumbnail of Effects of scandium addition in wrought aluminium alloys

A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a consi... more A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a considerable part of the available literature on Scandium in Aluminium alloys. Paper 2 and Paper 3 is a study of isothermal precipitation kineetics and mechanisms in a binary Al-Sc slloy. Precipitaion of the equilibrium phase A13Sc was found to occur either continuously or disontinuously, depending on teh temperature. Measurements of electrical conductivity were used to estimate the solvus line of SC in A1, and for estimating the interface energy between A13Sc particles and the A1 matrix.Paper 4 and Paper 5 are studies of alloys in the ternary A1-Mg-Sc and A1-Sc-Si systems, respectively. It was found that Mg had no marked influence on the precipitaion behavior of A13Sc, and the A13Sc particles were found to prevent recrystallisation of a deformed A1-Mg-Sc alloy even when it was heated to temperatures close to the solidus. Si, however, was found to have a strong influence on the precipitation hardening potential of A1-Sc-Si alloys. At 500°C the A13Sc particles were found to disappear with increasing Si level.In Paper 6 and Paper 7 the effects of adding Sc and Zr to an A1-Mg-Si alloy are explored. A13Sc particles could be formed during heat treatments at 550°C when at least 0.2 wt.% Sc was added by to the slloy. However, the highest number density of particles was achieved by adding both 0.2 wt.%Sc and 0.1wt.%Zr to the alloy. The A13Sc particles did not act as nucleation sites for Mg2Si, and the Sc addition to the alloy did not have any influence on the preciptation hardening of the alloy. In hot rolled material, one did not manage to identify A13Sc particles. In specimens that were hot rolled material, solutionised and then age hardened, the ductility was found to increase with increasing Sc level, while 0.4wt.%Sc was found to decrease the strength of the alloy somewhat.

Research paper thumbnail of Scandium in aluminium alloys

International Materials Reviews, Feb 1, 2005

A considerable part of the available literature on scandium in aluminium alloys is reviewed. Expe... more A considerable part of the available literature on scandium in aluminium alloys is reviewed. Experimental data and assessments of the binary Al-Sc phase diagram, a wide range of ternary Al-Sc-X phase diagrams and a few higher order phase diagrams are accounted for, with emphasis on the aluminium rich part of the diagrams. The phase which is in equilibrium with Al, Al 3 Sc, can form by several different mechanisms, all of which are described. The precipitation kinetics of Al 3 Sc in binary Al-Sc alloys are discussed, and an overview of the reported influences of ternary alloying elements on the precipitation of Al 3 Sc is given. The Al 3 Sc phase particles can serve as a grain refiner in the Al melt, a dispersoid for controlling the grain structure of the alloy and a strengthening precipitate. Several examples of these three effects are mentioned, both in binary Al-Sc alloys, and in more complex alloys. The reported effects of Sc on the precipitation behaviour in Al-Cu, Al-Mg-Si, Al-Zn-Mg and Al-Li alloys are also revised. A brief account of the effects of Sc additions on the corrosion behaviour of Al and Al-alloys is given. Finally, some views on the current and future use of Sc-containing Al alloys are given.

Research paper thumbnail of Precipitation in Some Dilute Al-Ge-Si Alloys

International Journal of Materials Research, Nov 1, 1995

Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respec... more Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respect to solvus temperatures, solid solubility at 400 °C and precipitation behaviour at 160 °C. Solvus temperatures were determined both by measurements of electrical resistivity and by scanning electron microscopy (SEM). The results of the two methods were fairly consistent. Specimens annealed at 400 °C were studied by SEM. The area fractions of the precipitates were measured, and used for calculations of the solid solubility of the alloys at this temperature. From the results obtained, one has proposed a most likely shape of the isothermal sections of the Al-rich solvus surface. Age hardening experiments showed an improved hardness in some of the ternary alloys, as compared to the binaries. However, it seems like all alloys are equally dependent on the quenched-in vacancies to facilitate nucleation of precipitates.

Research paper thumbnail of Effect of Low Cu Addition and Thermo-Mechanical History on Precipitation in Al-Mg-Si Alloys

Materials Science Forum, Jun 1, 2014

The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformat... more The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformation on precipitation hardening in two Al-Mg-Si alloys is investigated by transmission electron microscopy (TEM), and related to material hardness. Two alloys have been used, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes. A double peak hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. The 1% pre-deformation also made this effect less pronounced, but it led to faster initial hardness evolution and delayed over-aging. Maximum hardness was not influenced by cooling rate and the pre-deformation. Hardness was directly related to precipitate number densities.

Research paper thumbnail of Scandium In Aluminium Alloys: Physical Metallurgy, Properties And Applications

Metallurgical Science and Tecnology, Sep 5, 2013

The use of scandium as an alloying element in aluminium has gained an increasing interest even th... more The use of scandium as an alloying element in aluminium has gained an increasing interest even though scandium is difficult to extract, which makes the metal very expensive. The three principle effects that can be obtained by adding scandium to aluminium alloys are (i)grain refinement during casting or welding, (ii)precipitation hardening from Al 3 Sc particles and (iii)grain structure control from Al 3 Sc dispersoids. Addition of scandium in combination with zirconium is particularly effective, and the reason for this is linked to the recently discovered core/shell structure of the Al 3 (Sc,Zr) dispersoids. The effects that can be obtained from a Sc addition are to a large extent dependent on the alloy system to which it is added, and an overview of some effects in all the major classes of wrought aluminium alloys is given. Industrial use of Sc-containing aluminium alloy is so far limited to a few aerospace applications and to sporting equipment, further use is dependent on a price reduction of scandium. AL-SC MASTER ALLOYS When adding alloying elements to an aluminium melt, this can be done either by adding the pure elements or by adding the elements in the form of master alloys. Adding pure Sc to the melt is technologically feasible. From the binary phase diagram in Figure 2 [11, 16] it is evident that unless the melt is heated to a temperature higher than approx. 1185°C a sequence of phase

Research paper thumbnail of Precipitation in Some Dilute Al-Ge-Si Alloys

International Journal of Materials Research, 1995

Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respec... more Six Al-Ge-Si alloys with a constant solute content of 1.3 at.% have been investigated with respect to solvus temperatures, solid solubility at 400 °C and precipitation behaviour at 160 °C. Solvus temperatures were determined both by measurements of electrical resistivity and by scanning electron microscopy (SEM). The results of the two methods were fairly consistent. Specimens annealed at 400 °C were studied by SEM. The area fractions of the precipitates were measured, and used for calculations of the solid solubility of the alloys at this temperature. From the results obtained, one has proposed a most likely shape of the isothermal sections of the Al-rich solvus surface. Age hardening experiments showed an improved hardness in some of the ternary alloys, as compared to the binaries. However, it seems like all alloys are equally dependent on the quenched-in vacancies to facilitate nucleation of precipitates.

Research paper thumbnail of Al-Mg-Si billets with high extrudability – state of the art and beyond

Materials Today: Proceedings, 2019

Within the alloy groups EN-AW6060 and EN-AW6063 a range of alloys termed "High Speed Alloys". hav... more Within the alloy groups EN-AW6060 and EN-AW6063 a range of alloys termed "High Speed Alloys". have been developed. The underlying metallurgical principles of this development are explained. Further, new technological developments and new experimental discoveries have led to a new, upcoming billet quality, "HP 6xxx". Three different billet qualities, "Standard 6060", "High Speed 6060" and "HP 6060" were compared in a full-scale industrial trial, and the results indicate that the improvement in extrudability of "HP 6060" over "High Speed 6060" is of the same order as the improvement of "High Speed 6060" over "Standard 6060".

Research paper thumbnail of The Effect of Elastic Strain and Small Plastic Deformation on Tensile Strength of a Lean Al–Mg–Si Alloy

Metals, 2019

Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusio... more Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusion, the aluminium profiles are usually straightened, causing the material to be subjected to a small plastic deformation. This study demonstrates the positive effect on strength that can be obtained from such small deformation levels or from only elastically straining the material. Elastic straining of a lean Al–Mg–Si alloy, when performed immediately after solution heat treatment, enhances the material yield strength after artificial ageing to T6. Transmission electron microscopy shows that this effect can be attributed to a higher number density and finer dispersion of the age-hardening precipitate needles. Furthermore, introducing a small plastic deformation of 1% after solution heat treatment results in a comparable strength increase to elastically straining the material. In this case, however, the strength increase is due to the increased dislocation density, which compensates for a ...

Research paper thumbnail of The effect of alloying elements on the ductility of Al-Mg-Si alloys

Materials Science and Engineering: A, 2017

Experiments were conducted to attempt to understand the effect of different alloying elements on ... more Experiments were conducted to attempt to understand the effect of different alloying elements on the ductility of Al-Mg-Si alloys. Four alloys with different concentrations of Si, Mg, Fe, Mn and Cu were selected for examination. The strength-ductility relationship was evaluated by tensile tests, and microscopic analysis in light optical microscope, SEM and TEM was conducted to investigate grain-, constituent-, precipitatation-and fracture characteristics. Excess-Si (Mg/Si>1.73) was found to have a detrimental effect on the ductility of Al-Mg-Si alloys, without the presence of additional alloying elements. This alloy had an elongation to fracture of 23.1%, where failure occurred partly intergranularly, and was seemingly due to poor grain boundary characteristics. Adding Fe and Cu improved the ductility (and strength) to 42.9% elongation, and the change was related to the formation of secondary-phase particles, resulting in less free Si for embrittlement of grain boundaries. The best ductility, 79.2% elongation, was found by introducing Mn, which in addition to the above-mentioned changed

Research paper thumbnail of The effects and behaviour of Li and Cu alloying agents in lean Al-Mg-Si alloys

Journal of Alloys and Compounds, 2017

We show how replacing a fraction of Mg with Li in a lean Al-Mg-Si alloy gives comparable strength... more We show how replacing a fraction of Mg with Li in a lean Al-Mg-Si alloy gives comparable strength and enhanced temperature stability. Replacing solute with smaller amounts of Cu and Li also improves thermal stability and nearly compensates the strength loss for longer ageing times. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) documented Li and Cu causing modest structural changes to the main hardening precipitate, β". However, density functional theory calculations verified the observation from HAADF-STEM that Li preferentially occupies Mg3 sites in the β" structure.

Research paper thumbnail of The Effect of Heating Rate on the Density and Spatial Distribution of Dispersoids during Homogenisation of 6xxx Aluminium Alloys

Materials Science Forum, 2016

Two 6xxx alloys with different Mn-content have been homogenised in a furnace at 575 oC for 2 hour... more Two 6xxx alloys with different Mn-content have been homogenised in a furnace at 575 oC for 2 hours and 15 minutes. Three different heating rates to the homogenisation holding temperature were chosen, as this was expected to affect the precipitation behaviour of the dispersoids. The study focused on developing a reliable procedure for the characterization of the density and spatial distribution of dispersoids in aluminium alloys; both in terms of sample preparation, microscopic techniques and quantitative analyses of results. Scanning electron microscopy (SEM) has been used to evaluate the dispersoid characteristics for the different alloys and heating rates. The results indicate an increase in dispersoid number density and a more uniform distribution of dispersoids for the lowest heating rate, as compared to the more rapid heating rates, for the alloy with 0.05 wt% Mn. For the alloy with 0.15 wt% Mn the number density increased with the heating rate. This is suggested to be due to p...

Research paper thumbnail of Directionality and Column Arrangement Principles of Precipitates in Al-Mg-Si-(Cu) and Al-Mg-Cu Linked to Line Defect in Al

Materials Science Forum, 2016

In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that co... more In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that column surrounding of an element column in the needle/lath direction order according to simple principles. Advanced transmission electron microscopy and DFT calculations support the principles originate with a line defect, which is a segment of a <100>Al column shifted to interstitial positions. We propose the defect aids solute decomposition by partitioning the FCC matrix locally into columns of fewer and higher number of nearest neighbours, which suit smaller and larger size solute atoms, respectively. The defect explains how <100> directionality of the precipitates can arise in a cluster. Ordering of a few defects leads naturally to GPB zones in Al-Mg-Cu and to β'' in Al-Mg-Si.

Research paper thumbnail of Comparison of Properties of Extruded 6xxx Alloys in T5 Temper versus T6 Temper

In order to achieve the highest possible potential for age hardening in extruded profiles of 6xxx... more In order to achieve the highest possible potential for age hardening in extruded profiles of 6xxx alloys it is necessary to make sure that as much Mg and Si as possible is in solid solution before the ageing. This can be done either by a separate solution heat treatment, or by making sure that no (Mg,Si) particles are formed in the as-extruded profile prior to artificial ageing. The present paper explains how one can avoid (Mg,Si) particles in the asextruded profile, and the effect of billet preheating temperature is illustrated by an example from industrial scale experiments. Further, it is shown by examples from semi-industrial scale experiments with 6005 alloys that when precautions are taken to avoid (Mg,Si) particles in the as-extruded profile the T5 strength is at least as good as the T6 strength. In some cases a separate solution heat treatment may actually lead to a much lower strength in the T6 condition.

Research paper thumbnail of The Effect of Cu and Ge Additions on Strength and Precipitation in a lean 6xxx Aluminium Alloy

Journal of Physics: Conference Series, 2015

It has been demonstrated that the strength loss in a lean Al-Mg-Si alloy due to solute reduction ... more It has been demonstrated that the strength loss in a lean Al-Mg-Si alloy due to solute reduction could be compensated by back-adding a lower at % of Ge and Cu. Nanosized precipitate needles which are the main cause of strength in these alloys, and material hardness has been correlated to parameters quantified by TEM. It was found that additions of Ge and Cu strongly affect the precipitation process by increasing precipitate density and reducing precipitate size. Investigations of precipitate atomic structure by HAADF-STEM indicated that they contain mixed areas of known phases and disordered regions. A hexagonal Si/Ge-network was found to be present in all precipitate cross sections.

Research paper thumbnail of Effects of scandium addition in wrought aluminium alloys

A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a consi... more A series of seven papers is presented in this thesis. Paper 1 is a comrehensive review of a considerable part of the available literature on Scandium in Aluminium alloys. Paper 2 and Paper 3 is a study of isothermal precipitation kineetics and mechanisms in a binary Al-Sc slloy. Precipitaion of the equilibrium phase A13Sc was found to occur either continuously or disontinuously, depending on teh temperature. Measurements of electrical conductivity were used to estimate the solvus line of SC in A1, and for estimating the interface energy between A13Sc particles and the A1 matrix.Paper 4 and Paper 5 are studies of alloys in the ternary A1-Mg-Sc and A1-Sc-Si systems, respectively. It was found that Mg had no marked influence on the precipitaion behavior of A13Sc, and the A13Sc particles were found to prevent recrystallisation of a deformed A1-Mg-Sc alloy even when it was heated to temperatures close to the solidus. Si, however, was found to have a strong influence on the precipitation hardening potential of A1-Sc-Si alloys. At 500°C the A13Sc particles were found to disappear with increasing Si level.In Paper 6 and Paper 7 the effects of adding Sc and Zr to an A1-Mg-Si alloy are explored. A13Sc particles could be formed during heat treatments at 550°C when at least 0.2 wt.% Sc was added by to the slloy. However, the highest number density of particles was achieved by adding both 0.2 wt.%Sc and 0.1wt.%Zr to the alloy. The A13Sc particles did not act as nucleation sites for Mg2Si, and the Sc addition to the alloy did not have any influence on the preciptation hardening of the alloy. In hot rolled material, one did not manage to identify A13Sc particles. In specimens that were hot rolled material, solutionised and then age hardened, the ductility was found to increase with increasing Sc level, while 0.4wt.%Sc was found to decrease the strength of the alloy somewhat.

Research paper thumbnail of Effects of Germanium, Copper, and Silver Substitutions on Hardness and Microstructure in Lean Al-Mg-Si Alloys

Metallurgical and Materials Transactions A, 2015

It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be comp... more It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be compensated by adding back smaller quantities of Ag, Ge and Cu. Nine alloys were investigated. Ge was found to be the most effective addition, strongly refining the precipitation. The hardness is discussed in terms of statistics of the precipitates near a T6 condition, as acquired by transmission electron microscopy. Precipitates in some conditions were also investigated by high angle annular dark field scanning transmission electron microscopy. The added elements have strong influence on the main hardening precipitate, '', changing its structure and promoting disorder.

Research paper thumbnail of Some comments on the misfit and coherency loss of AlSc particles in Al?Sc alloys

Scripta Materialia, 2005

An attempt of refining a recently reported calculation of the temperature dependent misfit betwee... more An attempt of refining a recently reported calculation of the temperature dependent misfit between Al and Al 3 Sc particles is given. Further, the impact of a temperature dependent misfit on the calculated diameter for coherency loss of Al 3 Sc precipitates is demonstrated. The origin of misfit dislocations is also briefly discussed.

Research paper thumbnail of Effects of Sn Addition on Microstructure, Extrudability, Mechanical Properties and Machinability of a 6082 Alloy

Materials Science Forum, 2002

Research paper thumbnail of Effect of Low Cu Addition and Thermo-Mechanical History on Precipitation in Al-Mg-Si Alloys

Materials Science Forum, 2014

The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformat... more The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformation on precipitation hardening in two Al-Mg-Si alloys is investigated by transmission electron microscopy (TEM), and related to material hardness. Two alloys have been used, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes. A double peak hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. The 1% pre-deformation also made this effect less pronounced, but it led to faster initial hardness evolution and delayed over-aging. Maximum hardness was not influenced by cooling rate and the pre-deformation. Hardness was directly related to precipitate number densities.

Research paper thumbnail of Influence of Low Cu Addition on Quench Sensitivity in Al-Mg-Si Alloys

Advanced Materials Research, 2014

Quench sensitivity in two Al-Mg-Si alloys, one Cu-free and the other with low Cu additions (~0.1 ... more Quench sensitivity in two Al-Mg-Si alloys, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes, has been investigated using transmission electron microscopy (TEM) and corresponding material hardness. A two stage hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. However maximum hardness was not influenced by cooling rate, which could be related to higher precipitate number densities and volume fractions. Both alloys were over-aged faster in the slow cooling conditions.