| Summary: | 碩士 === 大葉大學 === 機械與自動化工程學系 === 97 === The purpose of this study for extrusion AZ80A magnesium alloy welds carry out solid solution and aging treatment, and discussion the precipitates type and distribution to welds micro structure and mechanical property influence situation. The experiment uses the alternating current inert gas tungsten electrode arc welding (TIG) way plate welding. Use the temperature 420℃ solid solution treatment and to keep the temperature 1 hour, and then use the 200℃ temperature, the time set 4, 8, 12, 16, 20 hours to carry out the aging treatment.
From the experimental results showed the welds to accompany the aging time increasing, these precipitates can effectively enhance the hardness of materials. Base and welds metal have the same type of precipitates, but the time, pattern and distribution of precipitates will be slightly different. The layer-shaped precipitate is the first emergence in base and welds metal. The precipitates can effectively enhance the micro-hardness, yield strength and maximum tensile strength, but the breakage way easily along precipitates interface separation, thus cause the elongation ratio to drop.
When layer-shaped precipitates transform to intermittent layer-shaped precipitates will be led to decline in yield strength, but the short-rod-shaped precipitates begin to precipitate help to enhance the yield strength in welds. The boundary precipitates keep growing, the breakage way easily along grain boundary and precipitates interface separation cause the elongation ratio to drop.
In the sum of the data analysis, the AZ80A magnesium alloy base and welds, use the 420 ℃-1hr solution heat treatment, after use the 200 ℃-4hr aging treatment will be get better of mechanical properties.
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