Effect of particle size on tool wear in friction stir welding of al 6061 with silicon carbide reinforcement

One major barrier to the implementation of metal matrix composites (MMCs) in structural applications is the problems which arise in joining these materials using fusion welding (fusion welded MMC joints are characterized by the presence of a deleterious intermetallic phase formed when the matrix material is melted). This phase is absent in friction stir welded MMC joints, but the FSW tool (which has a virtually unlimited life in unreinforced Aluminum alloys) wears rapidly as a result of contact between the tool and the harder reinforcement particles in the MMC. When applied to FSW of MMCs, Nunes’s rotating plug model for material flow in FSW predicts that the amount of wear depends on the size of the reinforcement, a prediction is tested in this study by embedding various size particles along the advancing side of the weld seam of an Al 6061 butt joint and assessing the resulting wear of the tool using three techniques: weighing, scanning electron microscopy (SEM), and contact profilometry. The results of this investigation demonstrate that material lost by the tool probe in FSW of MMCs is in direct proportion to the reinforcement particle diameter and that the change in the surface texture parameters of the probe is also correlated with particle size. It follows that wear in FSW of MMCs can thus be minimized by selecting materials with very small particulate inclusions.