Analysis of the effect of friction stir welding on the structure and properties of a new Al–Ca–Zn–Mg-based eutectic alloy
摘要
For sheet metal products with a thickness of 2 mm, fabricated using a new non-heat treatable eutectic alloy based on the Al–1Ca–5.5Zn–1.5 Mg system, a weld seam was obtained using friction stir welding. Scanning and transmission electron microscopy, as well as mechanical tests for hardness and uniaxial tension were used to study the fine structure and mechanical properties of the resulting weld seam and near-weld area. Analysis of the weld seam microstructure has revealed a deep refinement of the crystals of the eutectic phase (Al, Zn)4Ca (average particle size < 5 μm) along with their more uniform distribution across the cross–section in comparison with the base metal. There is a little difference between the structure in the center of the weld and the thermomechanically affected zone. Analysis of the hardness distribution profile in the weld seam cross-section has revealed a slightly higher hardness in the center of the mixing zone (HV117) compared to the base metal (HV110). TEM analysis of the microstructure shows the formation of a recrystallized structure with an average grain size of about 1 μm. Individual inclusions of insoluble Ca-containing crystals measuring less than 100 nm in size are found along the grain boundaries, suggesting their role as boundary migration barriers. The uniaxial tensile tests have shown that the ultimate strength of the weld seam samples is equal to that of the base metal (~330 MPa), leading to a conclusion about the strength factor being close to 1.