Solid State Renewable Az31 Magnesium Alloys

Magnesium alloy is widely used in automobile, communication, electronic and aviationindustries due to its low density, high specific strength, electromagnetic shieldingperformance, high vibrating load. The production and application of magnesium andmagnesium alloy has been quickly increasing and it is viewed as "the most promising greenmaterials in21stcentury". As the biggest magnesium country, how to effectively andcontinuously develop and use magnesium alloy is significant to the Chinese magnesiumindustry.Nowadays, the most-used methods of producing magnesium are casting, die-casting, andextrusion and so on. In the process of production, much waste and scrape is generated; at theend of life of magnesium products, they are needed to be recycled. Therefore, the technologyof recycling magnesium waste has been the key point of continuous development ofmagnesium. However the traditional re-melting has the disadvantages of easy-operating,small investment, much ignition loss, un-safety and environment-damaging, the newdeveloped method give a new way with the advantages of safety, low energy consumption andenvironment protection.In this paper, hot extrusion is employed to solid-recycle AZ31chips. The AZ31chipsused in this experimental is0.30-0.35mm thin and is from machine process of AZ31rode.Chips are pressed at room temperature with the pressure of70t and then heated up to varioustemperatures and hot-extruded by ratio25. the recycled samples later experienced necessarycharacterizations including metallographic analysis, tensile test and fracture analysis for thepurpose of investing the mechanism of recrystallization and the effect of temperature on theperformance of recycled samples. In addition, milling process is introduced in the traditionalhot extrusion method. After ten hours milling in air, AZ31chips are became thin, flat powderand then cold expressed and hot extruded at370℃. According the metallographic analysis,the distribution of oxide is demonstrated.The research results show that the chips interface is metallurgic ally bonded after hotextrusion by ratio25, and dynamic recrystallizaition is the main mechanism of deformation.The nucleation sites are interface of chips, boundary of big grains and DRX small grains and twins. At the extrusion ratio of25, grain refining has completed and the refined grain size isbelow3μm. Refined grain size don't exhibit distinct change during temperature from320℃-420℃, but grow bigger extremely after420℃, and reached20μm. Recycled AZ31possesses higher strength, and have the trend of increasing first and decreasing then. The peakstrength is305MPa at370℃. But the elongation is not satisfactory compared to cast sample.Elongation percentage is up to13.4%and down to9.3%. The low elongation can be explainedby the fracture surface, where the dominant mechanism is brittle mode with massive cleavagestepson and rive patterns. From the metallographic organization, oxide content is improvedgreatly for the introduction of milling. the distribution of oxide in the center region is irregularshaped with rough diameter of below50μm, and the boundary area is curve-shaped with gapof below10μm. This difference is owing to the unequal deformation.