Grain Refinement And Mechanical Properties Of AZ91Magnesium Alloy Processed By High-pressure And Low-temperature Sintering

Magnesium and Magnesium alloys, due to their high specificstrength and stiffness, low density, good thermoforming, gooddamping properties, good electromagnetic shielding and otheradvantages, play a very important role and get broad applicationprospects in automotive, electronics, electrical appliances,communications, aerospace and defense industry. However, the lowmechanical properties of magnesium alloy limit the application at thehigh end. For HCP Magnesium and Magnesium alloys, grainrefinement can effectively improve its mechanical properties. AZ91ingot was selected as the research materials, and was mechanicalground to prepare AZ91magnesium alloy powders in this paper. Then,AZ91alloy with compact structure, refined grains andgood performance was prepared by high-pressure andlow-temperature sintering.The microstructure evolution of AZ91alloy processed by high-pressure and low-temperature sintering was studied by meansof optical microscope (OM), X-ray diffraction (XRD) and scanningelectronic microscopy (SEM). The dynamic recrystallization, the grainrefinement and growth of AZ91alloy during high-pressure andlow-temperature sintering were investigated. The effect of sinteringtime on the density and hardness of AZ91alloy was also analyzed.Compared with cold press sintering, grains of AZ91alloyprocessed by high-pressure and low-temperature sintering under1200MPa and300℃were obviously fined, and a lot of smallβ-Mg17Al12particulates dispersed in the grain boundaries. With theincrease of high pressure and low temperature sintering time, smallgrains and the second phase has grown up in the alloy. AZ91alloy wassintered completely after48hours. The average grain size of thesintered alloy was about10μm.In high pressure and low temperature sintering process, thesintering time has a significant impact on density and hardness ofsintered body. The density of AZ91alloy processed by high-pressureand low-temperature sintering for1h was significantly improved, butpowders were yet not metallurgically bonded. The density of sinteringbody gradually increased with the increase of sintering time. Whenthe sintering time extended to48h, the relative density of the sinteredAZ91alloy were99.5%and the hardness of sintered alloy prepared by high-pressure and low-temperature sintering increases obviously,from81.6HV of the cast alloy to103HV.AZ91alloy with refined grains was prepared by high-pressureand low-temperature sintering, hoping to provide a new method forrecycling industrial magnesium alloy chips and the expansion ofhigh-performance magnesium alloy research.