強制氧化及熱機處理對鎂合金AZ91D固相回收製程之研究

Study on Forced Oxidation and Heat Treatment Against Magnesium Alloy AZ91D Solid State Recycle Process

國治(Jyh Gwo)

指導教授 ： 李雄

國立中央大學/工學院/機械工程研究所碩士在職專班/碩士(2007年)

摘要

鎂合金為最輕的結構金屬，因其具有良好的比強度、比剛性、導(散)熱性、制震性、電磁遮蔽性及材料回收性等優異的特性，因而被認為是3C產品機殼及汽車非結構材料的最佳選擇，廣泛應用於各種3C產業、汽車工業與自行車等需結構輕量化的工業上。
鎂合金工業因近年來的蓬勃發展，大量廢料及產品回收的問題日益凸顯，因目前業界所用的液相回收製程有著高污染、高耗能、高成本及高危險性等缺點，因此，開發鎂合金低耗能、低成本且符合世界環保潮流的固相回收製程技術已是刻不容緩；本文係屬鎂合金固相回收製程的研究，主要目的在於探討不同熱處理及熱機處理條件對其機械性質及微結構的影響，並找出鎂合金AZ91D氧化廢料固相回收的最佳製程參數。
本研究採用鎂合金AZ91D之新生屑料，以300℃強制氧化經350噸壓機於室溫壓密為預成形體後，再以350℃擠製溫度擠製成70mm x 10mm的鈑材；研究的結果發現：因強制氧化所造成的氧化層會在擠製過程中碎裂成強化相顆粒，故直接擠製的鈑材與規範相較，其抗拉強度提高24 %(達297.7MPa)，降伏強度提升1倍(達219MPa)，伸長率些微上升(達4.3 %)；擠製鈑材在170℃時效處理的部份，其最佳機械性質的尖峰時效約在16hrs，此時的抗拉強度達382.3MPa，降伏強度達269MPa，伸長率達5.6%；擠製鈑材在不同溫度的退火處理的部份，其機械性質並無明顯的變化，但伸長率由4.3%提升至6.7%，主要原因為塊狀的β相微細化所致；另擠製鈑材在不同熱機處理的部份，其最佳之熱機處理製程參數分別為(1)軋前350℃退火處理+軋後400℃退火處理(其抗拉強度為335.6MPa，降伏強度為233.5MPa，伸長率為8.1%)；(2)軋前415℃均質化處理+軋後350℃退火處理(其抗拉強度為343.4MPa，降伏強度為262.2MPa，伸長率為4.0%)，基於成本與時間的考量，本研究建議AZ91D氧化料固相回收材最佳之熱機處理製程為：軋前350℃退火處理+軋後400℃退火處理。

關鍵字

熱處理 ； 強制氧化 ； 固相回收 ； 鎂合金AZ91D ； 熱機處理

並列摘要

Magnesium alloy is a kind of lightest structure metal. As it has strong tensile stress and toughness, good conductivity and vibration absorber, electromagnetic cover and easy material recycling, magnesium alloy could be the best choice for 3C products for Aircraft chamber and automobile non-structure requirement material. It becomes wildly used in 3C manufacturing, automobile industry and bicycle etc. light structural industries.
Recently magnesium alloy developed very fast. Large dumping and product recycle problem becomes outstanding. Since the current recycled liquid state processes applied in the most industries are highly contaminated, highly energy exhausted, highly cost and highly hazardous, it is necessary to develop a low cost and low energy exhausted magnesium alloy recycle technology. The research work is to introduce how the solid-state magnesium alloy could be recycled. Various heat treatment approaches and different heat treatment conditions are selected to investigate into the alloy mechanical property and its microstructure performance. It is expected to find out the best result data to strengthen the magnesium alloy AZ91D solid-state recycle process.
The research work tries to collect many magnesium alloy AZ91D chips and put them into 300oC oxidation temperature to force them deformed into certain shape by mean of a 350 tons press machine. And then it will be shaped into 70mm x 10mm bar under the temperature 350oC.
The research work has reached certain interesting conclusions: As the forced oxidation layer material are crunched into tiny pieces during the press process, the final shaped bar has 24% higher tensile stress (297.7Mpa), 100% increased yield stress (219Mpa) and little increased extension rate (4.3%). When the shaped bar at 170oC tempering heat treatment process, the best mechanical property effect is at about 16hrs, excellent tensile stress 382.3Mpa, best yield stress 269Mpa and high extension rate 5.6%. The bar under various temperature tempering processes, the mechanical property effects vary a little, but extension rate could reach 6.7% from the original 4.3% because of the βparticles being crunched into small pieces. In addition, it is found that the best thermo-mechanical data are (a) 350oC pre-crunched process plus 400oC pro-tempering heat treatment. The tensile stress could reach 335.6Mpa, yield stress 233.5.2Mpa and extension rate 8.1%; (b) 415oC pre-crunch process plus 350oC pro-tempering heat treatment. The tensile stress could reach 343.4Mpa, yield stress 262.2Mpa and extension rate 4.0%. Considering the time and cost, it is suggested that (a) could be the best AZ91D solid-state recycle process.

並列關鍵字

Heat Treatment ； Forced Oxidation ； Solid-State Recycle Process ； Magnesium Alloy AZ91D ； Thermo-mechanical treatment

參考文獻

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