Abstract
Aluminium (Al) and titanium (Ti) coatings were applied on AZ91E magnesium alloy using a low-pressure warm spray (WS) method. The deposition was completed using three different nitrogen flow rates (NFR) for both coatings. NFR effects on coating microstructure and other physical properties were systematically studied. Microstructural characterization was performed using scanning electron microscopy (SEM), and the porosity was estimated using two methods—image analysis and X-ray microtomography. The coating adhesion strength, wear resistance, and hardness were examined. The protective properties of the coatings were verified via a salt spray test. Decreasing NFR during coating deposition produced more dense and compact coatings. However, these conditions increased the oxidation of the powder. Al coatings showed lower hardness and wear resistance than Ti coatings, although they are more suitable for corrosion protection due to their low porosity and high compactness.
Highlights
The low density of magnesium (Mg) alloys makes them an attractive alternative to aluminium (Al) alloys for various structural applications, especially in aerospace
A comprehensive comparison of Al and Ti coatings deposited using the warm spray (WS) on AZ91E magnesium alloy has been made
Both the substrate and metal powders used in the spraying process are sensitive to high temperatures, effective coatings were produced in both cases using the WS
Summary
The low density of magnesium (Mg) alloys makes them an attractive alternative to aluminium (Al) alloys for various structural applications, especially in aerospace. One of the limitations of the process is the difficulty in producing dense high-strength metal and alloy coatings because of the high critical velocity required to form bonds between deposited particles Another technique with solid potential for Ti and Al coating formation is warm spray (WS), an HVOF system modification developed and commercialized by the National Institute for Materials Science (Tsukuba, Japan) [26,27]. This method provides the advantage of process temperature control in the range of approximately 700–1900 K. Metallic powder materials can be deposited in a thermally softened state at high impact velocity It allows the forming of dense coatings with limited oxidation (in contrast to HVOF) and very low porosity. The average diameter of both powders was 37 and 32 μm for Al and Ti adequately
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