| Summary: | 碩士 === 大葉大學 === 醫療器材設計與材料碩士學位學程 === 106 === In recent years, the issue of renewable energy and environmental regeneration have been increased attention by industrial. With the demands of vehicle production and aerospace industry, light weight metals have gradually been used. Among them, magnesium alloy exists many excellent characteristic, but the behavior of ductility still low. There are also some problems in forming and welding. Therefore, how to improve the quality of magnesium products is quite important.
In this experiment, gas tungsten arc welding was used to test the welding of AZ91D magnesium alloy. After that, weldment was treated by solid solution and aged to explore the effect of aging parameters on the mechanical properties of the welds. From the result of welding tests show that, applying 19 amps alternating current can adequately penetrate the two mm thickness sheet. However, the mechanical properties of weld were inferior to the base metal. Therefore, it is hoped to improve the weldment properties by following solid solution and aging treatments.
When inspecting the 150℃ and 170℃ shorter aging time specimens, the shape of continuous and discontinuous lamellar precipitates appeared and able to enhance the hardness and tensile strength of welds, but show bad effects on elongation. Further detailed inspection the tendency of yield and tensile strength curves, the types and the amount of precipitates will continue increase with increasing aging time. Therefore, the trend of strength apparently rises first, then slows down, and declines at the end. As for the elongation and toughness curves, with increasing the amount of precipitates and their precipitation location, will hinder the mobility of dislocation. So the capability of plastic deformation continue to decrease, the curve shows the decline and flat tendency.
Based on experimental results, to perform aged treatment of AZ91D magnesium alloy welds, choosing 400℃-1 hour for solid solution, then following with 150℃-160 hours or 170℃-64 hours for aging treatment, can effectively improve the strength of welds. Also, specimen aged at 150°C will exist better whole nature performance.
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