Preparation Of Ultrafine-grained Mg-3Al-Zn-xAg Alloy And Rolling Deformation Behaviour

In this paper, four high-purity element powder Mg, Al, Zn, Ag were used to get Mg-3Al-Zn-x Ag(x = 0, 0.5, 1.0, 2.0) composite powder with different contents of Ag, obtained by high energy mechanical milling.The bar with the density of 99% could be acquired after the process of vacuum hot pressing and hot extrusion. In addition, rolling process, solution treatment and aging treatment were studied to obtain magnesium alloy sheets with good strength and ductility. The results of this study were as follows:The average grain and particle size of Mg-3Al-Zn-0.5Ag powder was the smallest, about 335 nm and 15.26μm.After hot pressing and warm extrusion, the density of material had a large improvement, which could reach to 95% and 99%, respectively, achieving the expected results of the experiment. In addition, in the extruded bars of containing 2.0 wt.% Ag, the weak characteristic peaks of Mg54Ag17 phase could be found in X-ray diffraction pattern, which described that the new phase Mg54Al17 was formed in the extrusion process.The effect of extrusion temperatures on the mechanical properties were investigated. It was found that the as-extruded bars had the best overall performance at 250℃. The results of tensile and compression properties of the materials of different Ag content showed that tensile strength and compressive strength of Mg-3Al-Zn-0.5Ag alloy were the highest, 428.93 MPa and 432.36 MPa, respectively. Subsequently, the grain size of the four-component alloys could be seen again by fracture analysis and may determine the fracture modes of alloys were quasi-cleavage fracture. Considering various factors, the best extrusion temperature was 250 ℃and the alloy composition is Mg-3Al-Zn-0.5Ag.In this paper, the initial rolling material was the extruded bars with a diameter of 18 mm.The key points of research were rolling temperature and reduction, which had a big impact on microstructure and properties of the sheet, including two reductions of 20%, 30% and three rolling temperatures of 250℃,300℃,350℃, for the purpose of getting reasonable rolling process of Mg-3Al-Zn-0.5Ag alloy. Finally, the best results were rolling temperature of 300℃ and reduction of 20%.At last, solution treatment and aging treatment were studied for magnesium alloy sheets. After solution treatment at 300℃ for 2h, the microstructure of sheets changed at different aging temperatures and time. The average grain size grew from 0.69μm to 1.4μm, which was about twice the original grain size. In various aging processes, the number, distribution and size of precipitates were different. The TEM analysis determined that the precipitated phase was Mg54Ag17 phase. It was found the strength, hardness and elongation of sheets could be improved simultaneously by choosing reasonable aging temperatures and time. The best effective treatment process was as follows: aging temperature of 140℃, aging time of 10 h. Under these conditions, the yield strength and tensile strength of the material could reach to 390.47 MPa, 457.98 MPa, with an elongation of 17.81%. After aging treatment, the fracture type was still quasi-cleavage fracture.