AZ91為常見之商業鎂合金，WZ73因具有LPSO長週期堆疊相而成為新型鎂合金材料。隨著鎂合金需求量逐年成長，可預期鎂合金切屑廢料量隨之上升，若能將切屑廢料有效利用，則可解決鎂合金廢料回收問題。本研究使用鑄造AZ91及WZ73合金加工後之切屑，以熱氫製程、高能球磨、球磨及熱氫複合製程將切屑處理成粉末後，將粉末熱壓成型，探討不同製程對切屑細化效果、微觀結構、熱壓成型機械性質之影響。
研究結果顯示，AZ91切屑熱氫製程中產生燒結現象使平均粒徑從146.5 μm上升至237.6 μm，熱氫製程後相能回到原本組成；WZ73切屑平均粒徑從144.8 μm下降至129.0 μm，熱氫製程中YH2相生成且無法放氫，造成LPSO相分解且無法重組。高能球磨有效將平均粒徑及晶粒尺度下降，球磨40小時之AZ91及WZ73粉末平均粒徑分別為21.5 μm和19.8 μm，平均晶粒尺度下降至22.4 nm和22.6 nm，WZ73切屑球磨過程中釔、鋅固溶至基材內，造成LPSO相分解且無法重組。熱氫、球磨製程後AZ91相皆能重組，WZ73中LPSO相則無法重組。球磨40小時之AZ91、WZ73粉末粒徑、晶粒尺度接近，WZ73粉末因LPSO相分解，AZ91粉末Mg17Al12強化相仍存在，造成AZ91熱壓試片強高於WZ73熱壓試片。球磨40小時之AZ91及WZ73粉末因粒徑尺度小且分佈均勻，在200 ℃進行熱壓成型之試片分別具有最高硬度184.1 HV、166.1 HV。經球磨40小時與熱氫製程之AZ91粉末再經熱壓成型後因產生HDDR過程而散佈大量Mg17Al12相在材料中，抗壓強度相對於未經熱氫製程試片高，具有最高抗壓強度541.9 MPa。經球磨40小時與熱氫製程之WZ73粉末再經熱壓成型後因散佈YH2相，造成硬度較高之Mg24Y5相無法生成，抗壓強度相對於未經熱氫製程試片沒有提升，因散佈相差異，AZ91熱壓試片強度高於WZ73熱壓試片。球磨過程中粉末受到大量撞擊，造成殘留應力產生，熱氫製程中產生退火效果，熱壓試片之壓縮應變量皆上升。

AZ91 is the common magnesium alloy in industry. WZ73 become a new type of magnesium alloy material due to LPSO phase. As the demand for magnesium alloys grows year by year, the amount increase of magnesium alloys scrap will be expected. The scrap recovery problem can be solved if the scrap waste can be effectively utilized. In this study, swarf of AZ91 and WZ73 alloys were used to investigate the effects of processes, which were processed by thermal hydrogen processing, high energy ball milling, ball milling and thermal hydrogen combined processing, and the powder molded by hot pressing. The effect of the alloys swarf refining, microstructure and mechanical properties of hot pressing are discussed.
The results show the average particle size of AZ91 swarf increased from 146.5 μm to 237.6 μm due to sintering effect in thermal hydrogenation processing, and the phases can recombine after thermal hydrogen processing. The average particle size of WZ73 swarf reduced from 144.8 μm to 129.0 μm, LPSO phase in WZ73 swarf was decomposed after thermal hydrogen processing whereas the YH2 phase formed, resulting in hydrogen cannot be desorbed. After ball-milled for 40 hours, AZ91 and WZ73 average particle size reduced to 21.5 μm and 19.8 μm, average grain size reduced to 22.4 nm and 22.6 nm, both the average size of particle and grain reduced by high energy ball milling. LPSO phase in WZ73 swarf was decomposed during the process of ball milling; where bismuth and zinc are segregated into grain boundary in the substrate. The phases in AZ91 can recombine after thermal hydrogen processing and ball milling, but LPSO phase in WZ73 can’t recombine after thermal hydrogen processing and ball milling. After ball-milled for 40 hours, the particle and grain size of AZ91 and WZ73 powder were similar, but AZ91 hot-pressed specimen strength was higher than WZ73 hot-pressed specimen, because LPSO phase in WZ73 decomposed after ball milling and AZ91 second phase Mg17Al12 was still in. After ball-milled for 40 hours, AZ91 and WZ73 powder because of small particle size, the hot-pressed at 200 °C has the best hardness of about 184.1 HV and 166.1 HV. After ball-milled for 40 hours and under thermal hydrogen processing, AZ91 powder hot-pressed specimen has higher compressive strength than hot-pressed specimen of ball-milled powder and a maximum compressive strength of 541.9 MPa, due to the dispersion of a large amount of Mg17Al12 phase by HDDR process. After ball-milled for 40 hours and under thermal hydrogen process, WZ73 powder hot-pressed specimen did not have higher compressive strength than hot-pressed specimen of ball-milled powder, due to the dispersion of a large amount of YH2 phase but less Mg24Y5 phase. Because the different of dispersed phase, AZ91’s data higher than WZ73’s. Thermal hydrogen processing provides the same effect as annealing, so the compression strain of hot-pressed specimen was enhanced.

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