The effect of main alloying elements on the physical properties of Al–Si foundry alloys (original) (raw)

Thermal description of hypoeutectic Al-Si-Cu alloys using silicon equivalency

Vojnotehni?ki glasnik, 2012

The modeling of casting processes has remained a topic of active interest for several decades, and availability of numerous software packages on the market is a good indication of the interest that the casting industry has in this field. Most of the data used in these software packages are read or estimated from the binary or multi-component phase diagrams. Unfortunately, except for binary diagrams, many of ternary or higher order phase diagrams are still not accurate enough. Having in mind that most of the aluminum binary systems are very well established, it has been tried to transfer a multi-component system into one well known Al-Xi pseudo binary system (in this case the Al-Si phase diagram was chosen as a reference system). The new Silicon Equivalency (Si EQ) algorithm expresses the amounts of major and minor alloying elements in the aluminum melts through an "equivalent" amount of silicon. Such a system could be used to calculate several thermo-physical and solidification characteristics of multi component as cast aluminum alloys. This lends the model the ability to make predictions of solidification characteristics of cast parts, where cooling rates are slow and the solidification process has to be known in great detail in order to avoid problems in the casting. This work demonstrates how the Si EQ algorithm can be used to calculate characteristic solidification temperatures of the multi-component hypoeutectic Al-Si-Cu alloys as well as their latent heats. SA statistical analysis of the results obtained for a wide range of alloy chemical compositions shows a very good correlation with the experimental data and the Si EQ calculations.

Thermal analysis during solidification of cast Al–Si alloys

Thermochimica Acta, 2010

Solidification of a series of aluminium alloys was studied by means of thermal analysis; the study was centred on the effect that silicon and iron exert on the temperatures for the onset of different microstructural characteristics. The alloys were prepared in a gas fired furnace and were poured into graphite moulds instrumented with a type K thermocouple. The cooling curve was registered with the aid of a computerdriven data logging system and was derived to determine the temperatures for the onset of the formation of pre-eutectic aluminium dendrites, and those for the Al-Si eutectic and for a complex Al-Si-Cu-Mg eutectic. It was found that silicon exerts a strong influence on the two former temperatures, whereas the third one is independent of the content of silicon or iron.

Measurements of electrical and thermal properties with growth rate, alloying elements and temperature in the Al–Si–X alloys

International Journal of Cast Metals Research, 2017

In this work, effect of alloying elements (X = Cu, Co, Ni, Sb and Bi) and growth rates on the microstructure, physical properties (electrical resistivity, enthalpy and specific heat) of the directionally solidified Al-Si eutectic alloy have been investigated. Al-12.6Si-2X (wt. %) samples were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified under constant temperature gradient, G (7.80 K/mm) and different growth rates, V (8.3-166.0 μm/s). Flake spacing (λ) and electrical resistivity (ρ) were measured from the solidified samples. The variation of electrical resistivity with temperature in the range of 300-500 K for alloying elements in the Al-Si eutectic cast alloy was also measured. The enthalpy of fusion (ΔH) and specific heat (C p) for the same alloy were determined by a differential scanning calorimeter from the heating curve during the transformation from solid to liquid.

Phases morphology and distribution of the Al-Si-Cu alloy

2009

AbstrAct Purpose: In this paper results of phase morphology investigation are presented of a newly developed Al-Si-Cu alloy. Such studies are of great interest for the metal casting industry, mainly the automotive industry, where improvement of cast elements quality is crucial for economic and quality reason and depends mainly on properly performed controlling process of the production parameters Design/methodology/approach: The basic assumptions of this work are realised with Universal Metallurgical Simulator and Analyzer. The solidification process itself is analysed using the UMSA device using the Derivative Thermo Analysis. Findings: During the investigation the formation of aluminium reach (α-Al) dendrites was revealed and also the occurrence of the α+β eutectic, the ternary eutectic α+Al 2 Cu+β, as well as iron and manganese containing phase was confirmed. This work shows that the thermal modification of the Al-Si-Cu can be quantitatively assessed by analysis of the microstructure evaluation as well as of the cooling curve thermal characteristics. Research limitations/implications: The investigations were performed using standard metallographic investigation as optical, scanning and transmission electron microscopy methods; also the EBSD phase identification method based on the kikuchi lines identification was used. The results in this paper are valuable only for the Al 2 Cu, Fe and Mg containing phases, and are not performed for the assessment of the Silicon Modification Level. Practical implications: As an effect of this study it will be possible to understand and to influence the mechanism of structure forming, refinement and nucleation. Also better understanding of the thermal characteristics will be provided to achieve a desirable phase morphology required for specific application of this material under production conditions. Originality/value: The originality of this work is based on applying of regulated cooling rate of aluminium alloy for structure and mechanical properties changes. In this work the dependence among the regulated cooling speed, chemical composition and structure of the investigated aluminium cast alloy on the basis of the thermoanalysis was presented.

Mechanical properties as a function of microstructure and solidification thermal variables of Al–Si castings

Materials Science and Engineering: A, 2006

The aim of the present study was to investigate the influence of solidification thermal variables on the as-cast microstructure of hypoeutectic Al-Si alloys and to establish correlations with the casting mechanical properties. Experimental results include transient metal/mold heat transfer coefficients, tip growth rate, local solidification time, secondary dendrite arm spacing, ultimate tensile strength and yield strength as a function of solidification conditions imposed by the metal/mold system. It was found that the ultimate tensile strength increases with increasing alloy solute content and with decreasing secondary dendrite arm spacing. Yield strength seems to be independent of both alloy composition and dendritic arrangement. Such results have permitted general expressions correlating dendrite spacing with transient solidification processing variables to be established. The correlation of such expressions with experimental equations relating the ultimate tensile strength and dendrite spacing provides an insight in the preprogramming of solidification in terms of mechanical strength of Al-Si castings. Predictive theoretical and experimental approaches for dendritic growth have been compared with the present experimental observations.

Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al-13% Si alloy

Materials Science and Engineering …, 2003

For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al Á/13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting/chill interfacial region. The corresponding interfacial heat flux transients and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing.

Assessment of Post-eutectic Reactions in Multicomponent Al-Si Foundry Alloys Containing Cu, Mg, and Fe

Metallurgical and Materials Transactions A, 2015

Post-eutectic reactions occurring in Al-Si hypoeutectic alloys containing different proportions of Cu, Mg, and Fe were thoroughly investigated in the current study. As-cast microstructures were initially studied by optical and electron microscopy to investigate the microconstituents of each alloy. Differential scanning calorimetry (DSC) was then used to examine the phase transformations occurring during the heating and cooling processes. Thermodynamic calculations were carried out to assess the phase formation under equilibrium and in nonequilibrium conditions. The Q-Al 5 Cu 2 Mg 8 Si 6 phase was predicted to precipitate from the liquid phase, either at the same temperature or earlier than the h-Al 2 Cu phase depending on the Cu content of the alloy. The AlCuFe-intermetallic, which was hardly observed in the as-cast microstructure, significantly increased after the solution heat treatment in the alloys containing high Cu and Fe contents following a solid-state transformation of the b-Al 5 FeSi phase. After the solution heat treatment, the AlCuFe-intermetallics were mostly identified with the stoichiometry of the Al 7 Cu 2 Fe phase. Thermodynamic calculations and microstructure analysis helped in determining the DSC peak corresponding to the melting temperature of the N-Al 7 Cu 2 Fe phase. The effect of Cu content on the formation temperature of pAl 8 Mg 3 FeSi 6 is also discussed.

Structure investigation of the Al-Si-Cu alloy using derivative thermo analysis

2009

Purpose: This research work presents the investigation results of derivative thermoanalysis performed using the UMSA device (Universal Metallurgical Simulator and Analyzer). The material used for investigation was an Al-Si-Cu alloy known as AC-AlSi7Cu3Mg grade aluminium cast alloy. Design/methodology/approach: As a result of this research the cooling rate influence on structure and mechanical properties changes, especially HB Hardness was investigated. The cooling rate was set in a variable range of ~0.2 ºC/s to ~1.25 ºC/s. In this work structure changes were determined concerning the structure, especially the dendrites and grains and particle distribution in the aluminium matrix. Findings: The reason of this work was to determine the optimal cooling rate values, to achieve good mechanical properties for protection of this aluminium cast alloy from losing their work stability and to make it more resistant to action in hard working conditions. For investigations of the aluminium samples hardness measurements of the different sample areas were performed. The material was examined metallographically and analyzed qualitatively using light and scanning electron microscope as well as the area mapping and point-wise EDS microanalysis. The performed investigation are discussed for the reason of an possible improvement of thermal and structural properties of the alloy. The investigation revealed the formation of aluminium reach (α -Al) dendrites and also the occurrence of the α+β eutectic, the ternary eutectic α+Al 2 Cu+β, as well the occurrence of the Fe and Mn containing phase was confirmed. Practical implications: In the metal casting industry, an improvement of component quality depends mainly on better control over the production parameters. Originality/value: This work provides also a better understanding of the thermal characteristics and processes occurred in the new developed near eutectic Al-Si-Cu alloy. The achieved results can be used for liquid metal processing in science and industry and obtaining of a required alloy microstructure and properties influenced by a proper production conditions.

A correlation to describe interfacial heat transfer coefficient during solidification of Al-Si alloy casting

A thin wall Al-9 wt.% Si alloy casting was made in a sand mold prepared by CO 2 process. The thermal history obtained from the experiment was used to solve an inverse heat conduction problem (IHCP). The IHTC was estimated by an iterative algorithm based on the function specification method. Acquired IHTC values are given as a function of time and as a function of the casting surface temperature at the interface. It has been found that pattern of IHTC variation with casting surface temperature can be described by an equation which has been proposed as a new correlation model. In order to verify broader applicability of the proposed correlation, its use is demonstrated on the IHTC results taken from the literature. © 2012 Elsevier B.V. All rights reserved.