The microstructure, mechanical properties and fracture behavior of as-cast Mg-10Gd-3Y-xZn-0.6Zr (x = 0, 0.5, 1 and 2 wt%) alloys have been investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and tensile tests. The experimental results reveal that the microstructure of the alloy without Zn contains α-Mg and Mg24(Gd,Y)5 phase, the microstructure of the alloy with 0.5% Zn contained of α-Mg, (Mg,Zn)3(Gd,Y) and Mg24(Gd,Y,Zn)5 phase, whereas when Zn content was 1% and 2%, the Mg12(Gd,Y)Zn phase and some needle-shaped stacking faults notably appear and the Mg24(Gd,Y,Zn)5 phases completely disappear. Moreover, a new 18R long period stacking ordered (LPSO) phase is observed in grain boundaries with increasing Zn content up to 2%. The tensile tests indicate that the alloy containing 0.5% Zn shows the optimal mechanical properties and the ultimate tensile strength (UTS), yield strength (YS) and elongation are 228MPa, 172MPa and 5.1%, respectively. As indicated by fracture analyses, the fracture modes of the alloys with 0%, 1% and 2% Zn are brittleness transcrystalline fracture, and the tensile fracture mode of 0.5% Zn alloy is typical tough transgranular fracture.

The purpose of the present study is to model and analyze heat treatment process of Al-Si-Mg alloy prepared by indirect squeeze casting. The combined effects of whole heat treatment process, including solution treatment temperature, solution treatment time, ageing temperature and ageing time, on Vickers hardness, were investigated. The non-linear mathematical model has been developed through Box-Behnken design based on response surface methodology. The results of ANOVA tests have proven the model is capable of making accurate predictions and statistically adequate. The significance tests show all four process parameters significantly affect response value and the relationship might be non-linear in nature. The dimensional response surface and matching contour plots are drawn, establishing an evaluation of the interaction effects of process parameters. The optimum heat treatment process is found as solution treatment temperature of 540.28ºC, solution treatment time of 7.55h, ageing temperature of 174.23ºC, and ageing time of 8.61h.

Aluminum alloy is the important alloy which has been widely used. To reduce waste, it is necessary to thixoform these alloys in near net shape. Semi-solid slurry is the key in process. In this work, the semi-solid slurry of ZL101 aluminum alloy was prepared by using serpentine channel. Effect of process parameters on the microstructure of semi-solid ZL101 aluminum alloy produced by serpentine channel was investigated. The results show that, the morphology of primary α-Al grains transformed from rosette to spheroid with decreasing pouring temperature. Satisfied semi-solid slurry of ZL101 aluminum alloy was prepared with pouring at 630°C to 670°C. Increasing curve number can improve the morphology of primary α-Al grain and decrease grain size with same pouring temperature. Desired slurry can be obtained with the lower pouring temperature when serpentine channel is preheated. It can make the primary nucleus gradually evolve into spherical and near-spherical grains with the effect of “self-stirring” in serpentine channel and chilling.