Welding of cast A359/SiC/10p metal matrix composites

Abstract

Welding of metal matrix composites (MMCs) is an alternative to their mechanical joining, since they are difficult to machine. Published literature in fusion welding of similar composites shows metallurgical problems. This study investigates the weldability of A359/SiC/10p aluminum SiC MMC. Statistical experiments were performed to identify the significant variables and their effects on the hardness, tensile and bending strengths, ductility, and microstructure of the weld. Finite Element Analysis (FEA) was used to predict the preheat temperature field across the weld and the weld pool temperature. Welding current, welding speed, and the preheat temperature (300-350??C) affected the weld quality significantly. It was seen that the fracture of the welded specimens was either in the base MMC or in the weld indicating a stronger interface between the weld and the base MMC. Oxides formation was controlled along the weld joint. Low heat inputs provided higher weld strengths and better weld integrity. It was found that the weld strengths were approximately 85% of the parent material strength. The weld region had higher extent of uniform mixing of base and filler metal when welded at low currents and high welding speeds. These adequate thermal conditions helped the SiC particles to stay in the central weld region. The interface reaction between the matrix and SiC particles was hindered due to controlled heat inputs and formation of harmful Al4C3 flakes was suppressed. The hardness values were found to be slightly higher in the base metal rich region. There was no significant loss in the hardness of the heat affected zone. The ductility of the weld was considerably increased to 6.0-7.0% due to the addition of Al-Si filler metal.