Investigations of laser clad, thermal sprayed and laser remelted AlSi20-coatings on magnesium alloy AZ31B under constant and cycling thermal load

Magnesium alloys need to be coated for applications exhibiting mechanical or chemical loads. Al-based coatings with Si reinforcements have proven to be a suitable coating choice to offer good wear and corrosion protection. Especially in the automotive and aviation industry, the demand for lightweight construction materials such as Mg alloys is permanently growing. In some of these applications, like engine components, in passenger cars or shell parts in jet engines, Mg parts might also be exposed to thermal shocks or elevated temperatures. Laser clad, thermal spray and laser remelted thermal spray coatings made of AlSi20 were generated on magnesium alloy AZ31B. In order to qualify these coatings for applications exhibiting thermal loads, samples were exposed to 190 °C, 300 °C and 400 °C for time periods of 3 h to 144 h. Thermal shock testing was performed in a cycling heating (200 and 300 °C) and cooling (27 °C) with a cycle length of approx. 14 s. Increasing temperature and increasing heat exposure time period led to increasing diffusion between the coating and the substrate with formation of brittle Mg2Si. This led to the formation of cracks and pores under thermal loading which consequently resulted in delamination of the coating. The laser remelted thermal spray coatings behaved similar to the as-sprayed coatings since the layers were not melted. The results show that the performance of the AlSi20 coatings depends strongly on the coating process.