等通道轉角擠型製程參數對鎂粉固化塊材顯微組織與機械性質之影響

Abstract

本實驗使用-200mesh大小、平均粉末粒徑約為74μm的鎂粉，並選擇銅棒作為鎂粉容器來進行ECAE製程，在200℃、250℃、300℃的溫度下以路徑BC擠型一次、二次、四次。將得到的鎂粉塊材以SEM觀察其顯微組織並使用阿基米德法量測密度，接著做微硬度與壓縮試驗測試，最後進行腐蝕浸泡實驗。 結果顯示，鎂粉理想密度為1.88 g/cm3，而經過不同溫度與擠型道次ECAE製程的鎂粉塊材在溫度300℃且擠型道次為N=4時，密度可達到最高值1.85 g/cm3，為理想密度的98.4%。 微硬度方面，當溫度300℃且擠型道次為N=4時，微硬度可達到最高值49Hv，在300℃, N=4時孔洞率僅有1.6%；在200℃、250℃、300℃, N=4時，氧化物聚集大小的平均粒徑分別為29.14、21.16、14.95μm，因此當溫度從200℃增加至300℃時氧化物分散較均勻，可得到最高微硬度值。 壓縮試驗方面，200℃、250℃、300℃, N=4的最大抗壓應力分別為155MPa、175MPa、190MPa，壓縮降伏應力分別為75MPa、85MPa、100MPa，在300℃, N=4強度最大， 腐蝕浸泡實驗方面，200℃、250℃, N=4以及300℃, N=1, 2, 4的氧化程度(面積比例)分別為42%、39%、38%、34%、31%，且可觀察到腐蝕會先從顆粒邊界及顆粒與氧化物接觸介面開始發生，而300℃, N=4氧化程度最低，因此粉末間鍵結強度(Bonding)最高。

In this research, microstructure and mechanical behaviors of bulk magnesium consolidated from magnesium powder by equal channel angular extrusion (ECAE) were investigated. Particle size of magnesium powder was about 74μm in diameter. Magnesium powder was filled into copper cans then ECAEd for 1, 2 and 4 passes via Bc route at 200℃, 250℃ and 300℃, respectively. Microstructure of as ECAEed samples was observed by SEM. Density of each sample was carried out by Archimedes law. Microhardness, compression test and immersion corrosion test were conducted to investigate the properties of each ECAEed sample. Maximum density of bulk magnesium is 1.85 g/cm3 achieved after 4 passes of ECAE at 300℃. Magnesium powder is softer and more ductile at higher temperature; therefore, it is more easily to be deformed and filled into pores between partilces. ECAE process deforms and fines magnesium powder to fill residual pores, hence pores are eliminated by filling of magnesium powder. Maximum hardness value of bulk magnesium is 49 Hv achieved after 4 passes of ECAE at 300℃. It is due to the elimination of pores and the more uniform dispersion of oxides of samples at higher temperature. After 4th pass of ECAE at 200℃, 250℃ and 300℃, ultra compressive stress (UCS) of consolidated bulk magnesium achieved 155MPa, 175MPa and 190MPa. Compressive yield stress (CYS) of consolidated bulk magnesium achieved 75MPa, 85MPa and 100MPa, respectively. It is due to the more uniform dispersion of oxides of samples at higher temperature. After immersion corrosion for bulk magnesium of 4 passes at 200℃ and 250℃ and 1, 2 and 4 passes of ECAE at 300℃, degree of corrosion are 42%, 39%, 38%, 34% and 31%. Corrosion will take place initially between Mg and MgO interface. Best bonding strength between powders is achieved after 4 passes of ECAE at 300℃.