添加鎢酸鈉對AZ31鎂合金微弧氧化層生長機制與抗磨耗能力之研究

Abstract

本研究以雙脈衝電源於 AZ31 鎂合金表面進行微弧氧化製程，探討添加鎢酸鈉在矽酸鹽系統微弧氧化製程中對氧化層成膜機制的影響，並透過圓盤球式磨耗試驗機進行乾燥狀態下的抗磨耗能力比較。 實驗結果顯示，鎢酸鈉的添加超過5g/L時會使 AZ31 微弧氧化膜在矽酸鹽製程中出現兩個階段的成長行為。第一階段透過相對低熔點相MgWO4的併入束縛電漿化的氣體，進而吸引貫穿形式的B-type放電造成微弧氧化層的不均勻生長。第二階段則轉為孔洞內放電使膜層緻密並均勻增厚。適當的鎢酸鈉添加量能透過此二階段成長使微弧氧化膜表面富含較多高硬度之Mg2SiO4，進而擁有較好的抗磨耗能力，過多的添加量則會導致第一階段的膜層因強放電發生崩解，造成最終膜層厚度不均使抗磨耗能力劣化。

The micro-arc oxidation using a bipolar power supply was carried out and coated on AZ31 magnesium alloy. This study discussed the change of coatings' growth mechanism by adding sodium tungstate in a silicate-based electrolyte system. Meanwhile, the ball-on-disc wear test was applied to investigate the wear resistance in dry conditions. According to the experiment results, Adding sodium tungstate beyond 5g/L leads to a two-step coating growth. In the first stage, the incorporation of melton MgWO4 entraps the plasma gas to attract the penetrating B-type discharge, resulting in a non-uniform coating growth. Later, the second stage discharge in pores densifies and thickens the coating uniformly. Appropriate addition of sodium tungstate enriches the coating with more high hardness Mg2SiO4, thereby enhancing the wear resistance. However, excessive addition makes the coating collapse due to the intense discharge in the first stage, resulting in a non-uniform coating thickness and reducing its wear resistance.