Materials Science Forum Vols. 706-709

Abstract: In this present work, the microstructure and properties of an Al-7.5Zn-1.5Mg-1.4Cu-0.12Zr alloy forging in T7452 condition has been investigated by means of OM, TEM and EBSD analysis and varied properties test. The results indicate that there are obvious differences in grain morphology, precipitation characteristics and recrystallization degree along the thickness direction of the forging. The strength of the alloy forging is stable and varies less than 10% along the thickness direction. The alloy forging in the T7452 condition shows high strength, high toughness and good corrosion resistance, with the UTS, TYS, elongation and electrical conductivity values being 500~530 MPa, 460~500 MPa, 7.0~15.0% and 23.9~24.2 MS/m, respectively, and the fracture toughness in L-T, T-L and S-L direction being 33.5~39.5, 25.5~27.0, 23.0~24.5 MPa.m^1/2, respectively, and the EXCO rating being EA.

Abstract: The AA 7150-T351, in the form of 40 mm thick plates, was subjected to single-stage aging leading to peak aged condition, and two selected multi-artificial aging treatments leading to the over aged conditions. The microstructural differences along the thickness direction of the AA 7150-T351 plate were investigated using OM and electron backscatter diffraction (EBSD) technique, and the microstructural characterization was studied at different stages of multi-artificial ageing process by transmission electron microscopy. Tensile properties and electrical conductivity measurements were used to evaluate the property homogeneity along the thickness direction of the plate under various artificial aging tempers. It was revealed that the microstructural features and tensile property are inhomogeneous in different layers along the thickness direction, and both grain structure and tensile property exhibit appreciable anisotropy at the same thickness layer. The volume fraction of recrystallized grain of T351 plate in the near surface layer is higher than that in the center layer remarkably. It is also shown that two selected multi-artificial aging tempers can provide optimal precipitates in matrix and at grain boundaries, which gives rise to a combination of high strength and stress corrosion cracking (SCC) resistance in such materials.

Abstract: The quench sensitivity of 2D70 aluminum alloy was investigated by end-quenching. The effect of water temperature on quench sensitivity was studied by measuring the hardness and conductivity. The end-quenching characteristics of hardness and conductivity of 2D70 aluminum alloy under different water temperatures has been described. The end-quenching characteristics of 2D70 and 2124 alloy under the same condition have been compared and analyzed. The results show that the susceptibility of 2D70 alloy to quenching is slow and the differential effects of the water temperatures of 16°C and 30°C on end-quenching of this alloy are not obvious. The quench depth of the alloy is more than 150mm.

Abstract: In the present work we report on the effect of pre-deformation followed by/together with artificial aging on the mechanical properties as strength, ductility and work hardening of an Al-Mg-Si alloy (AA6060). The AA6060 alloy was initially cast, homogenized and extruded according to standard industrial practice. The extruded material was then subjected to a solution heat treatment and subsequently artificially aged after (sequential mode) and during (simultaneous mode) various combinations of deformation (0-10%) and heat treatments. The aging behaviour and mechanical properties have been characterized in terms of Vickers hardness and tensile testing. It is found that small, even very small, pre-deformations strongly affect the aging behaviour and associated tensile properties. Moreover, it is found, that with the carefully chosen parameters of simultaneous deformation and aging one can reach mechanical properties superior to those following pre-deformation and subsequent aging (sequential mode). The results are compared and discussed in view of differences in processing conditions and microstructure characteristics.

Abstract: It has been known that Cu- or Ag-addition Al-1.0mass%Mg₂Si (balanced) alloys shows higher hardness and elongation than Cu-free or Ag-free balance alloy. In this study, the alloys with Cu or Ag addition and the alloys with Si / Mg in excess have been investigated by hardness and tensile tests and HRTEM observation. Cu addition is effective for higher hardness, and Ag-addition is useful for improvement of elongation for peak-aged samples. Precipitates in peak aged these alloys have been confirmed by HRTEM. Cu-addition alloy almost includes Q’-phase, and Ag-addition alloy includes b’-phase. The precipitation sequence of Ag- or Cu addition Al-Mg-Si alloy was investigated using HRTEM, SAED, and EDS. The precipitates obtained in the two alloys were classified into several kinds by HRTEM images and SAED patterns. The relative frequencies of precipitates were also investigated and compared with that in the alloy.

Abstract: Effect of equal channel angular pressing (ECAP) at room temperature and subsequent annealing at temperatures ranging from 450 to 600°C on microstructure, mechanical properties and electric conductivity of an Al-8%Ce alloy was examined It was shown that Al₄Ce-type eutectic particles having plate-like shape break under ECAP; distribution of the particles appears to be more homogeneous. ECAP leads to about two-fold increase in yield stress (YS) and ultimate tensile strength (UTS); ductility and electric conductivity decrease significantly. Under following annealing, the spheroidizing and coagulation of Al₄Ce-type particles occur extensively resulting in decreased strength and increased electric conductivity and ductility.

Abstract: Aluminum foam is porous material and it is superior property which is light weight , absorption sound, heat insulation and energy absorption than other materials. In present the panel of aluminum foam sandwich panel to use as structural materials is adhered with adhesive or wax for adhesion. The aim of this study is to clarify producing conditions to make sandwich panel by melt drag process. Melt drag process is single roll strip casting process. Producing aluminum alloy strip and adhering foam are at a time.

Abstract: A combined method of electric contact heating and diffusion connection of steel-aluminum is proposed which makes; an essential effect on three-phase shaping conditions, provides better physical contact and contact surface cleaning, formation and conservation of solid setting units. Activation of contact surfaces is achieved more effectively and quickly than at mechanical and vacuum treatment. Formation of physical contact and setting corresponds to contemporary conceptions of solid body model and kinetics of development of connection strength by the data of the carried out tests. Mechanical testing is carried out in static and dynamic modes, structure and phase composition in steel-aluminum joint is determined.

Abstract: The effects of pre-aging before natural aging on the bendability of an asymmetric-rolled Al-Mg-Si alloy were investigated. In the specimen without pre-aging, hardness increased with natural aging time due to the formation of nanoscale cluster (nanocluster; Cluster (1)). The suppression of Cluster (1) during natural aging is clearly seen in the pre-aged specimens though the formation of Cluster (2). It was found that tensile properties were not so affected by the types of clusters. Bending test clearly showed that the pre-aging improves the bendability of this alloy. This effectiveness of pre-aging means Cluster (2) well contributes the deformability of this alloy compared with Cluster (1). Such an improvement of bendability is considered to be derived from the structure of nanoclusters and its interactions with the factor of plastically deformation of alloys.

Abstract: Al6061 alloys are well known as extrusion materials for automobile parts, aircraft. Recently, increasing demands of the lightweight for vehicles, materials have replaced steel are developed. Aluminum alloys are increasingly used as structural materials but in terms of mechanical properties, it is not a completed as a replacement for steel. The purpose of this study was to improve the mechanical properties and minimize the grain sizes of Al6061 matrix alloys for structural materials as produced by spray casting. Al6061 alloys were melted with 800°C in electrical resistance furnace. In order to form equilibrium concentration of Mg₂Si (about 2 times) for Al6061, increased Mg and Si were added to Al6061 alloys and then preforms were prepared with molten metal by spray casting. The Specimens were fabricated by solution heat treatment and T6 age hardening. As a result of analyzing microstructure observations and mechanical properties according to supersaturated solid solution of Mg₂Si for the final sample obtained, there were no changes in the size of the precipitates but precipitates per unit area were found to increase the area during the heat treatment processes. Mechanical properties such as tensile strength of over 80MPa and hardness of over 10HRB in spray casting have been increased according to solubility of Mg₂Si.