Similar and dissimilar friction stir welded joints made from AA2124+25% SiC and AA2024

An aluminium matrix composite (AMC) consisting of an AA2124 matrix reinforced by 25 vol.% SiC particles was used to produce similar AMC+AMC and dissimilar AMC+2024-T3 joints by friction stir welding. When the particle reinforced composite was located on the retreating side, material mixing was less intense for dissimilar joints. Nevertheless, a higher strength has been determined for this arrangement due to a hook-like interlocking of both materials. Tensile test and S-N fatigue behaviour is shown to be compromised by alignment of the reinforcement particles perpendicular to loading direction already in the particle reinforced base material. Welding residual stresses were determined through the cut-compliance method in terms of stress intensities acting at the crack tip. The underlying residual stress distribution in the un-cracked structure was calculated by the weight function method. Longitudinal tensile residual stresses were found to be higher in the monolithic material as compared to the particle reinforced composite. This held true both for similar and within dissimilar joints. Growth behaviour of cracks crossing the joint line was described and correlated with residual stresses for similar joints.