Wear resistance performance of AlCrN and TiAlN coated H13 tools during friction stir welding of A2124/SiC composite

Tool wear during friction stir welding (FSW) of hard particulate reinforced aluminum metal matrix composites (Al MMCs) are more prominent due to the tool interaction with the particulates at high strain rate. Considering the excellent mechanical and wear resistance properties of cathodic arc PVD coatings, they are expected to abate the wear of tools during FSW of Al MMCs. Hence, it is the aim of this study to investigate the contribution of cathodic arc PVD deposited AlCrN and TiAlN coatings in alleviating tool wear during FSW of Al MMCs. AlCrN and TiAlN coated H13 FSW tools were used to butt weld 8 mm thick aluminum alloy 2124 reinforced with 17 vol% SiC of 3 μm particle size. Interestingly, the coated tools exhibited significant improvement in wear resistance of about 92 and 80%, respectively, over the bare H13 tool. Over 97% reduction in the wear of the FSW tool was recorded during the plunging stage with the use of the coated tools. Additionally, AlCrN and TiAlN coated tools considerably improved the surface finish of the welded Al MMC. The coated tools demonstrated superior wear resistance due to the improved scratch crack resistance, high mechanical and oxidation resistance properties of the coatings. Dominant wear mechanisms on AlCrN and TiAlN coated tools were abrasive erosion and chipping off by sharp and hard SiC particles while severe striation and oxidation characterized the wear mechanism of the bare tool. The use of these coatings did not deteriorate the weld properties, rather some improvement in the hardness of the nugget zone was observed due to the characteristic dynamic stirring and refinement of the Al matrix and SiC particles.