The Effect of High-Temperature Eutectic-Forming Impurities on Aluminum 7108 Weldability (original) (raw)
Influence of scandium on weldability of 7010 aluminium alloy
Science and Technology of Welding and Joining, 2005
The commercial 7000 series aluminium alloys are based on medium strength Al-Zn-Mg and high strength Al-Zn-Mg-Cu systems. The medium strength alloys are weldable, whereas the high strength alloys are non-weldable. This is because the amount of copper present in these alloys gives rise to hot cracking during solidification of welds. As a result, the high strength Al-Zn-Mg-Cu base alloys are not used for applications where joining of components by welding is an essential step. In the present study, using a combination of qualitative Houldcroft test and quantitative Varestraint test, it is shown that a small addition of scandium to the commercial 7010 alloy reduces the hot cracking susceptibility during solidification of welds produced by the gas tungsten arc welding process. The improvement in weldability is found to be the result of the considerable grain refinement in the weld structure following the scandium addition. The results of microhardness and tensile tests are further described within the context of the present work to demonstrate that the 7010zSc welds also exhibit a combination of improved strength and ductility.
Effect of Cu and Mg contents on similar and dissimilar welding of 7XXX series aluminum alloys
This research discusses the various effects of alloying elements specially Cu and Mg contents on the weldability of Al-Zn-Mg-Cu-based alloy (7xxx series). Five series having different chemical compositions have been adopted. Both similar and dissimilar fusion welded joints have been made through various combinations of such alloys. Examination of mechanical properties of the welded joints; tensile strength and hardness values were carried out coupled with microstructure examination for the alloys before and after welding. This research could explain the effects of alloying additions; Cu and Mg, on the weldability of Al-Zn-Mg-Cu- based alloys. Increasing Cu content to about 2.83 wt% with almost zero Mg showed the best tensile strength either in similar or dissimilar welded joints. Same results could be obtained with maximum content of Mg: 2.42 wt% and almost zero Cu. Increasing both Cu and Mg contents to 2.42 wt% and 2.53 wt%, respectively in the same time deteriorated the tensile strength for similar and dissimilar welded joints. Welding of Al-Zn- Mg-Cu alloy has an inverse relation with combined increase of Cu and Mg content while it has a direct relation with single increase of either Cu or Mg alloying addition.
Metals
In this work, weldability and hot cracking susceptibility of five alloy 718 investment castings in laser beam welding (LBW) were investigated. Influence of chemical composition, with varying Si contents from 0.05 to 0.17 wt %, solidification rate, and pre-weld heat treatment were studied by carrying out three different weldability tests, i.e., hot ductility, Varestraint, and bead-on-plate tests, after hot isostatic pressing (HIP) and solution annealing treatment. Onset of hot ductility drop was directly related to the presence of residual Laves phase, whereas the hot ductility recovery behaviour was connected to the Si content and γ grain size. LBW Varestraint tests gave rise to enhanced fusion zone (FZ) cracking with much more reduced heat-affected zone (HAZ) cracking that was mostly independent of Si content and residual Laves phase. Microstructural characterisation of bead-on-plate welding samples showed that HAZ cracking susceptibility was closely related to welding morphology. ...
Studying the Effect of Precipitation Hardening on 6061 Aluminum Alloy Weldments
Advanced Materials Research, 2016
The high specific strength, ease of working, good weldability and the ability to be precipitation strengthening have increased the demand of aluminium alloys in aerospace and automobile industries. In this research the effect of artificial aging/precipitation hardening on mechanical properties and microstructures of 6061 aluminum alloy weldments produced using gas tungsten welding (TIG) was studied. The artificial aging of welded alloy was carried out at temperatures varying from 150°C to 170°C for different period of time. The Vickers hardness and tensile test were carried out to evaluate the response of material to heat treatment. The experimental work showed that the maximum hardness and tensile strength of 6061 aluminum welded samples was achieved when aged at 170°C (after solution treatment) for 2 and 10 hours. Scanning electron microstructure analysis revealed that after solution treatment, when the samples were aged at 150-170°C, the Mg2Si precipitates present in the grains g...
Journal of Materials Engineering and Performance, 2013
This work is concerned with the structure of the FSW joint of 2017A/7075 aluminum alloys, which was analyzed on the basis of a number of longitudinal and cross-sectional sections. Various ways and degrees of alloy stirring were identified, depending on the distance from the face of the weld. Furthermore, considerable variation in the length of the weld microstructures was demonstrated, reflecting the variability of the welding process. Studies of mechanical properties are also presented-the distributions of hardness on individual layers. A significant effect of plastic deformation on the hardness of the alloy 7075, which strengthened in deformed areas and shows weakness in the heat-affected zone, was noticed. The influence of the weld structure on the fracture of the sample, which was broken in the static tensile test, was analyzed applying scanning electron microscopy. The presence of non-deformed areas was revealed within the ductile fracture of the sample.
Journal of Materials Research and Technology, 2021
7000 series aluminum alloys have particularly high strength, if compared to other aluminum alloys or even to some high strength steels. Currently, this alloy is considered on the next developments of automotive structures, as an enabler of improved mechanical and safety properties, associated with weight reduction, supporting the industry to fulfill fuel economy and greenhouse gases emissions regulations. Due to the proneness to hot cracking and welding embrittlement, the joining of 7000 series sheets is limited to mechanical methods, such as self-piercing rivets. In order to provide the automotive industry with more joining methods suitable for the proposed high strength aluminum alloy, the objective of this work is to validate the resistance spot welding process of the AW-7075 alloy. The work is split in two parts: the preliminary assessment of the suitability of current welding procedures, norms and respective parameters, where the process window, weld nugget quality and electrode life-time are evaluated. Then an innovative approach is investigated, where the use of an upslope welding schedule, CuAg0.1 electrode caps, increased force and lower overall electric resistance could successfully validate the application, attending manufacturing requirements regarding welding quality, electrode life-time and process window. The resultant microstructure characteristics were analyzed with metallographic micro-sections and the phases were determined with the electron backscattered diffraction technique.
Journal of Materials Processing Technology, 2003
Weld solidification cracking in age-hardenable aluminium alloys is usually minimised by adjusting weld metal composition. One way of reducing cracking susceptibility is to refine the weld metal microstructure, which offers the additional benefit of improving mechanical properties. In the current work, grain refinement was achieved in weld fusion zones of a medium-strength Al-Zn-Mg alloy through inoculation with Ti, Ti + B and Zr. It was found that the grain structure in the refined welds was equiaxed in all three dimensions and that this led to a reduction in hot cracking tendency and to an improvement in hardness and tensile properties, especially ductility.
Possibilities to modify the properties of the AW7075 aluminum alloy for the automotive industry
Combustion Engines, 2024
Possibilities to modify the properties of the AW7075 aluminum alloy for the automotive industry ARTICLE INFO The paper investigated the AW7075 aluminum alloy that is used in the automotive industry. The alloy is widely used, among others, in the production of heads and engine blocks. The possibility of obtaining various properties of the alloy (material states) by appropriate heat treatment (saturation and aging) was demonstrated. The results of strength, hardness, abrasion, and fracture toughness tests of the alloy in the T73, RRA, and HTPP aging treatments, in comparison with the T651 reference state, are presented. The need to select the appropriate parameters of heat treatment in relation to the load conditions of the structural element, especially in elements with notches, was indicated. Depending on the state of the AW7075 alloy, the results prove the wide and diverse possibilities of its use and should be used consciously in the design and production processes of modern automotive drivetrain components.
Influence of Compositional Modifications on Thermal Stability of Alloy 718
Superalloys 718, 625, 706 and Various Derivatives (1994), 1994
Conventional Alloy 718 is compared to a modified alloy (976M) heat treated either with the usual heat treatment applied to Alloy 718 or with a specific heat treatment giving rise to the compact morphology microstructure. This comparison is made on the basis of hardness measurements and microstructural modifications resulting from long term aging (10 000 hours) applied at three temperatures (650°C-700°C-75O'C). It is shown that wathever the initial heat treatment is, the modified alloy has a better thermal stability than Alloy 71.8. A significant improvement is found at 7OO'C and 75O'C. Precipitate size and morphological evolution as well as volume fraction of delta phase has been measured as function of aging conditions. Tensile tests have been performed at temperatures ranging from room tempemture to 75O'C. The results show that the tensile properties of the modified alloy are better than those of Alloy 7 18. btroduction Alloy 718 is currently used as a disc material in gas turbine jet engines. The number of structural applications would undoubtly be increased if one could succeed in improving the high temperature fatigue crack growth resistance and the thermal stability of this material. The work reported in this paper is concerned with the latter objective. After solution treatment at temperature (5 .lOOO"C) and a conventional aging treatment (72O"C-811-AC.SO"C/h-620"C-8h) this alloy is strengthened by two types of precipitates, y'(Ni3(Al, Ti)) and y"(Ni3Nb). It may also contain the stable phase 6 (Ni3Nb) precipitated along the grain boundaries. The TTT diagrams published by Brooks and Bridge [l] and by Radavich [2] show that the sequence of precipitation depends on the solution heat treatment. The former authors indicate that y' precipitates are formed before y during the isothermal treatment while Radavich has proposed the inverse sequence. From these different behaviours one can conclude that it is difficult to control the precipitation of 'y phases without a modification of the chemical Superalloys 718,625,706 and Various Derivatives Edited by E.