硼酸濃度對AZ31鎂合金微弧氧化塗層抗磨耗性能之影響

Abstract

鎂合金與其他金屬相比具有相對較低的密度、優良的比強度和可回收性等優點，然而由於較低的硬度使鎂合金的耐磨耗性能較差，在工業應用上經常受到限制，因此必須進行適當的處理以提升表面的抗磨耗能力。 微弧氧化是近年來備受關注的一種表面改質技術，其塗層具有高硬度、耐磨耗和與基材附著性高等優點，但同時微弧氧化塗層表面的高粗糙度以及多孔性質嚴重影響了其耐磨耗性能，因此本研究藉由在矽酸鹽基溶液中添加不同濃度硼酸(2 g/L, 5 g/L)，以試圖改善微弧氧化塗層的緻密性及摩擦性能，提升其抗磨耗能力。 實驗結果表明，在基礎製程溶液中添加2 g/L的硼酸能使其塗層結構更為緻密並有助於耐磨耗性能提升，但當硼酸濃度增加至5 g/L時，由於放電現象的增強使得塗層孔隙率增加，導致塗層在較重負載下的耐磨耗性能顯著下降。通過在濃度5 g/L硼酸溶液中額外添加1.5 g/L的氫氧化鈉使溶液導電度下降，藉此降低製程中的擊穿電壓，成功使塗層孔隙率降低並且其塗層在所有試樣中表現出最好得耐磨耗性能。

Magnesium alloys compared to other metals have several advantages such as lower density, excellent specific strength, and recyclability. However, their industrial application is often limited due to their relatively low hardness and poor wear resistance. Therefore, appropriate surface treatments are necessary to enhance their performance. Micro-arc oxidation (MAO) is a surface modification technique that has gained significant attention in recent years. It offers benefits like high hardness, wear resistance, and excellent adhesion to the substrate. However, the high roughness and porosity of the micro-arc oxidized coating severely affect its wear resistance. In this study, different concentrations of boric acid (2 g/L, 5 g/L) were added to a silicate-based solution to improve the density and tribological properties of the coating. The experimental results indicated that adding 2 g/L of boric acid to the base process solution resulted in a denser coating structure, which contributed to enhanced wear resistance. However, increasing the boric acid concentration to 5 g/L led to an increased porosity due to intensified discharge phenomena, significantly reducing the wear resistance under heavier loads. By adding an additional 1.5 g/L of sodium hydroxide to the 5 g/L boric acid solution, the conductivity of the solution was reduced. As a result, this approach decreased the breakdown voltage during the process, effectively lowering the coating''s porosity. This led to a significant improvement in wear resistance, outperforming all other samples in the study.