Hardening And Annealing Transformation Kinetics Of AZ91 Alloy Smelted Directly From Crude Magnesium And Compressed At Room Temperature

Many fields have been looking for materials with better comprehensive properties. Magnesium alloy is the first choice with its excellent compreshensive property, such as low density, high specific strength and specific stiffness and easy recycle, etc. AZ91alloy is a commonly commercialized magnesium alloy, owing to his low cost and an excellent combination property. It is well known that magnesium alloy has a higher comprehensive properties after plastic deformation after being deformed.In this paper, the experimental samples are subjected to solution treatment, compression processing at room temperature and annealing. The microstructure, chemical compositions, rock-well hardness and micro-hardness of solid-solution, solution + compression, solution + compression + annealing AZ91 alloy were investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), rock-well hardness and micro-hardness tester, respectively. And precipitation kinetics ofβ-Mg₁₇Al₁₂ phase in deformed and non-deformed AZ91 alloys after annealing were also studied.The results shown that lots of twining would emerge as a result of compression at room temperature, most of which intersect with respect to each other at near 90o, serving as beneficial nucleation condition both forβ-Mg₁₇Al₁₂ phase precipitation and static recrystallzation. Theβ-Mg₁₇Al₁₂ phase precipitated preferentially at twin and grain bounbaries. In the annealing process, phase precipitation and growth were frequently observed at the intersection between twinning and original grain, or among various twinnings. The twin boundaries will get wider gradually with longer aging time and increasing temperature; Meanwhile, certain orientation relationships were also discovered between theβ-Mg₁₇Al₁₂ phase precipitated in twinning and theα-Mg matrix under 250℃annealing.When the deformation was 8%, no recrystallzation occurred under (250³50)℃×2h annealing condition. When the deformed to 10%, static recrystallzation started considerably after annealing at 350℃. The activation energy forβ-Mg₁₇Al₁₂ phase precipitation in AZ91 alloy was calculated to be 23.8³7.9kJ/mol using the JMAK equation, in accordance with our experimental data. The hardness of AZ91 alloy can be greatly related to compressing rate, precipitate amount, annealing temperature and time, etc.