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Abstract：The effect of homogenization on the hardness, tensile properties, electrical conductivity and microstructure of as-cast Al-6Mg-0.4Mn-0.25Sc-0.12Zr alloy was studied. The results show that during homogenization as-cast studied alloy has obviously hardening effect that is similar to aging hardening behavior in traditional Al alloys. The precipitates are mainly Al 3 (Sc,Zr) and Al 6 Mn. When homogenization temperature increases the hardness peak value is declined and the time corresponding to hardness peak value is shortened. The electrical conductivity of the alloy monotonously increases with increasing homogenization temperature and time. The decomposition of the supersaturated solid solution containing Sc and Zr which is formed during direct chilling casting and the precipitation of Al 3 (Sc, Zr) cause hardness increasing. The depletion of the matrix solid solubility decreases the ability of electron scattering in the alloy, resulting in the electrical conductivity increased. Tensile property result at hot rolling state shows that the optimal homogenization treatment processing is holding at 300−350 for ℃ 6−8 h.

The fatigue crack growth rate, fracture toughness and fatigue S-N curve of 2124-T851 aluminum alloy at high cycle fatigue condition were measured and fatigue fracture process and fractography were studied using optical microscopy (OM), X-ray diffraction (XRD) technique, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that at room temperature and R = 0.1 conditions, the characteristics of fatigue fracture could be observed. Under those conditions, the fatigue strength and the fracture toughness of a 2124-T851 thick plate is 243 MPa and 29.64 MPa · m 1/2 , respectively. At high cycle fatigue condition, the higher the stress amplitude, the wider the space between fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area, and the greater the ratio between the intermittent fracture area and the whole fracture area.

The influence of aging treatment on microstructure, mechanical and electrical properties of 7A52 alloy was investigated by mechanical property test, electrical conductivity measurement, XRD and TEM analysis. The results showed that the alloy was a typical aging hardening alloy. During aging supersaturated solution decomposed, G.P. zones and η'(MgZn2) precipitated. The precipitates of the alloy aging at 100°C were mainly G.P. zones with the size of about 5nm. During aging at 120°C, η’ precipitates nucleated from the G.P. zones. With increasing aging temperature and time, the size and amount of η' increased. As aged at 120°C for 24h the tensile strength, yield strength, elongation and electrical conductivity of the alloy were 496 MPa, 445 MPa, 9.5% and 26 %IACS, respectively. The G.P. zones and η' dispersion strengthening are the major strengthening mechanisms for the studied alloy at the single-stage peak aging.

The texture, microstructure, plastic strain ratio r value, elongation, strain hardening index n, the value of cupping test IE, and the correlation between r value and the other formability indices of two automotive aluminum alloys sheet 6016 and 6181, and commercial pure aluminum sheet were investigated. The results showed that the recrystallization textures of three aluminum alloys sheet are similar to each other, which mainly contain cube component. However, the r and n value, elongation, and IE of three aluminum alloys sheet are different from each other evidently, and there is no correlation between texture and r value, and the other formability indices except the n value. The large quantity of second-phase particles in the aluminum alloy matrix has very important effect on both the r value and the formability of aluminum alloy sheet.