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ABSTRACT
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.
Keywords: friction stir welding, metal matrix composites, abrasive particles, wear of materials
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1. INTRODUCTION
The application of friction stir welding (FSW) to Metal Matrix Composites (MMCs) is attractive because the process occurs at solid-state, thus precluding development of the deleterious theta phase formed when the molten Aluminum matrix reacts with reinforcement particles (Prater, 2011). Storjohann et al. (2005) first demonstrated that FSW-ed MMC joints are free from the intermetallic phases profligate in fusion welding of these materials. The high strength to weight ratio of MMCs as well as their impact resistance make them particularly attractive for aerospace applications and there has been some work by NASA to investigate the feasibility of welding them in aerospace structures (Ding et al., 2006). Tool wear represents the primary barrier to joining MMCs to themselves or other materials using FSW; as such, understanding tool wear is...