The effect of rolling and heat treatment on microstructure and mechanical properties of Mg3.5Y0.8Ca0.4Zr alloy was investigated. With the addition of 0.4Zr, the average grain size of the as-cast alloy was markedly refined to 5-10 μm. After hot rolling process, the grain size of Mg3.5Y0.8Ca0.4Zr alloy was refined further into 3-5 lain and the tensile strength was enhanced while the plasticity was degraded because the accumulation of rolling reduction increased the density oft-wins, and refined the grain structures. After the solution heat treatment at 743 K, the elongation of alloy was greatly enhanced from 3% to 17%.
Mg matrix composites with SiC particles ranging from 5vol%-25vol% were prepared using stirring casting method. Die casting, squeezing casting, and extrusion were applied for inhibiting or eliminating the defects such as gas porosity and shrinkage void. Through die casting and squeezing casting, most of the defects in Mg matrix composites could be eliminated, but the mechanical properties were improved limitedly. On the other hand, after hot extrusion, not only most of the defects of as-cast composites ingots were eliminated, but also the mechanical properties were improved markedly. With the addition of SiC, the tensile strength, yield strength and elastic modulus of as extrusion SiCp/AZ61 composites increased remarkably, and the elongation decreased obviously.
The （submicron ＋ micron） SiCp-reinforced magnesium matrix composite was fabricated by stir casting. After the application of forging and extrusion, the interface between SiCp and Mg in the composite was investigated by transmission electron microscopy. Results show that the interfacial characterization was different at the interfaces of micron-SiCp/Mg and submicron-SiCp/Mg. While most interfaces between micron-SiCp and Mg were clean, the precip- itated Mg17A112 phase as well as dispersedly distributed nano-MgO particles was observed at some interfaces. Unlike the interface between micron-SiCp and Mg, no interfacial reaction product was found at the interface between submicron-SiCp and Mg in the present study. Besides, the specific orientation relationships were found at the interfaces between submicron- SiCp and Mg, which was thought to have developed during hot deformation process. At the fracture surface of the composite, the microcracks were found at the interface between micron-SiCp and Mg, while the interfacial bonding between submicron-SiCp and Mg was very well.
Kun Kun DengJian Chao LiJian Feng FanXiao Jun WangKun WuBing She Xu
Good ignition-proof principle and mechanical properties were realized in Mg-Y-Ca-Zr alloy system.By adding Y and Ca elements,the ignition point of Mg-3.5Y-0.8Ca alloy was improved to over 1173 K,and the alloy could be melted in air without any protections.The ef-fect of Zr addition on the microstructures and mechanical properties of Mg-3.5Y-0.8Ca alloys were investigated,and Mg-3.5%Y-0.8%Ca-0.4%Zr alloy had good comprehensive properties with tensile strength of 190 MPa and elongation of 11%.Auger electron spectros-copy（AES） and X-ray diffraction（XRD） analysis revealed that the oxide film formed on the surface of Mg-3.5Y-0.8Ca alloy was mainly composed of Y2O3.Thermogravimetric measurements in dry air indicated that the oxidation dynamics curves measured at 773,873 and 973 K followed the cubic law.Moreover,the semiconductor characteristic of Y2O3 film and its effect on ignition-proof properties of Magnesium al-loys were discussed from the viewpoint of electrochemistry.
FAN JianfengCHEN ZhiyuanYANG WeidongFANG ShuangXU Bingshe
