冷噴銲處理對AZ80鎂合金表面性質之影響

Abstract

鎂合金的化學性質活潑，屬於易遭受腐蝕的金屬，因此防蝕處理成為鎂合金在應用的過程中所需探討的重要課題。本研究探討利用冷噴銲處理在AZ80鎂合金表面噴銲IN265、301不銹鋼、純鋁膜層後對AZ80鎂合金表面性質之影響，包括顯微組織、機械性質及腐蝕性質。 研究結果發現，在微觀結構及機械性質方面，冷噴銲處理形成的膜層為非緻密的膜層，在膜層內部會有少許孔隙。冷噴銲純鋁會使得AZ80鎂合金表面有明顯加工硬化的現象，故造成AZ80母材表面硬度值提升；冷噴銲IN625及301不銹鋼會使得AZ80鎂合金表面產生再結晶現象，造成鎂合金表面晶粒細化；而由於高溫及再結晶現象，晶粒內差排數量減少，故使得AZ80母材表面硬度值僅有些微上升。在磨耗試驗上，冷噴銲膜層皆提高了AZ80鎂合金的耐磨耗性，以IN625膜層抗磨耗性最佳，301不銹鋼膜層次之，再者為純鋁噴銲層。 在腐蝕性質方面，在NaCl水溶液環境中，IN625膜層及301不銹鋼膜層皆大幅提升了AZ80母材抗蝕性；且從循環極化曲線可看出IN625膜層及301不銹鋼膜層對孔蝕的再癒合能力佳，對於抗蝕性極差的AZ80鎂合金有大幅的改善。在泥漿沖刷的環境中，不論膜層或母材在低角度沖蝕中造成的破壞會大於高角度沖蝕，但不論於何種沖刷角度，IN625膜層、301不銹鋼膜層及純鋁噴銲層皆大幅提升了AZ80母材抗沖蝕性。 另外，經熱處理後的冷噴銲純鋁試片，在膜層與AZ80母材的界面處會產生交互擴散形成連續相之介金屬化合物，Mg17Al12及Al3Mg2，其硬度皆高於基材與噴銲層。而將AZ80鎂合金經冷噴銲純鋁粉後再進行陽極處理，可在試片表面得到一層高硬度氧化鋁層，此氧化層大幅改善了純鋁膜層在NaCl水溶液環境中的抗蝕性。

It is commonly recognized that magnesium possesses poor corrosion resistance because of its high oxidation potential and porous oxide structure. The corrosion resistance is the most important topic for magnesium alloys application. The thesis aims to investigate how cold spray influences the properties of magnesium alloy, including microstructure, mechanical and corrosion property. The sprayed substrate is AZ80 magnesium alloy. IN625, 301 stainless steel and aluminum powder is used to spraying on the surface. In the study, the coating formed by cold spray treatment has some holes, and is a non-dense film. AZ80 substrate occurred grain refinement after spray IN625 and 301 stainless steel process. For the aluminum coating, it was observed that after coating process, substrate surface is obviously harder than after coating IN625 process. As to the corrosion behavior, the result of the potential-dynamic polarization curve tests reveals that, whether in the IN625 or the Al coating, the corrosion resistance are better than magnesium substrate. In the wear and erosion test, the cold spray coating are to improve the wear and erosion resistance of AZ80 magnesium alloy. After annealing, the AZ80 alloy interacts with Al coating to form Mg17Al12 and Al3Mg2 compound at the interface. After anodizing, on the aluminum coating surface formed a high hardness alumina layer that has excellent corrosion resistance than aluminum coating.