Study On Preparation Technology Of AZ91D Magnesium Alloy By Solid-State Recycling

As the prevalent application of magnesium alloy, it become more and more important for the recycling of magnesium alloy to recycle scraps appropriately, save resource, reduce cost, prevent pollution of environment and prolong the lifetime.The methods of recycling magnesium alloy include solid-state and liquid-state recycling. The liquid-state recycling method is applied prevalently nowadays, which is complicated and unsafe since magnesium alloy are readily oxidized. This problem can be solved by solid-state recycling. The AZ91D magnesium alloy samples are prepared by hot extruding from machined chips. This method is safe without protective covering and fusion, which is based on plastic deformation theory, dynamic recrystallization and dynamic recovery mechanism, dispersion strengthening and diffusion welding mechanism.The study designed a set of mould with the extrusion ratio of 4:1,11:1,25:1,40:1,100:1, modular angle of 60?, 6mm of working tape, and 2°of rounding at the entrance of mould. It can meet the property test of materials prepared by hot extrusion from recycled machined chips, which is according to the design principle of extrusion mould.The AZ91D magnesium alloy was prepared by changing chip size, extrusion temperature, and extrusion ratio. The microstructure was observed; the mechanical property was tested, and compared with as-cast and the samples prepared by hot extrusion from cast ingot.The result shows that: compared with the as-cast AZ91D magnesium alloy, the grain is refined obviously since dynamic recrystallization have taken place in the process of hot extrusion; with extrusion temperature increasing, the grain becomes coarser in the range of 300℃~450℃. At 400℃,the microstructure is the most homogeneous, the tensile strength is the biggest and reaches 340.3MPa, and the elongation is 9.5%; with extrusion ratio increasing, the deformation of metal increases, the grains refine and the tensile strengthen increases. When the extrusion ratio is 100:1, the strength reaches 394.3MPa. when the extrusion ratio is below 25:1, with extrusion ration increasing, the elongation increases, when the extrusion ratio is above 25:1, with extrusion ratio increasing, the elongation decreases; with chip size decreasing, oxidation dispersed phase in the material increase, which causes grain refined and the tensile strength increased, when the size of chips is (1~1.5)mm×1mm×0.5mm, the tensile strength reaches 363.5MPa, but with the increasing of extrusion ratio, the elongation decreases because the oxidation dispersed phase causes nucleating of cavities readily, compared with AZ91D magnesium alloy prepared by hot extrusion from cast ingot(the tensile strength is 335.4MPa and the elongation is 12%), although the grain is finer and the tensile strength is higher, the elongation is 45% lower.