Morphology and Mechanical Properties of Titanium-based Coatings on AZ91

Magnesium alloys with proper protective coatings are finding wide applications. In this work, the morphology and mechanical properties of titanium-based coatings on magnesium alloy AZ91 have been studied. Pure Ti, Ti-11Al, Ti-47Al and Ti-6Al-4V coatings were deposited in a DC magnetron sputter unit. Scanning electron microscopy (SEM) observation of the coatings shows the presence of various defects including pinholes, cracks, and pores. The micro-hardness as well as corrosion behaviour of the coatings were examined. It has been found that the corrosion resistance was severely degraded by coating defects such as cracks. Cross-sectional SEM observation revealed that thickness of the coatings falls in the range of 3-6um and generally, the Ti-6Al-4V and the Ti-11Al coatings are thicker than the Ti-47Al and the pure titanium coatings. The measured hardness of the coatings falls between 36 and 46 HV, decreasing in the order of Ti-6Al-4V, Ti-11Al, Ti-47Al and pure Ti.