Heat-affected zone

About: Heat-affected zone is a research topic. Over the lifetime, 18787 publications have been published within this topic receiving 231744 citations.

A thermal model of friction stir welding applied to Sc-modified Al–Zn–Mg–Cu alloy extrusions

Abstract: A thermal model of friction stir welding is presented that proposes an energy-based formulation of the Johnson–Cook plasticity model in order to account for heat generation due to plastic deformation. The proposed formulation is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature of the alloy and the welding energy. The thermal model is applied to Sc-modified Al–Zn–Mg–Cu alloy extrusions joined by friction stir welding at 225, 250, 300 and 400 RPM (all other weld parameters held constant). With the incorporation of heat generation due to plastic deformation, the thermal model accurately predicts the maximum weld temperatures and temperature profiles at the higher energy weld conditions, i.e. 300 and 400 RPM. At the lower energy welds (i.e. 225 and 250 RPM) where plastic deformation contributes a larger portion to the total heat generation, the model under-predicts the maximum weld temperatures under the tool shoulder but shows good agreement with the remaining experimental temperature data.

Microstructure and mechanical properties of friction stir welded AA6092/SiC metal matrix composite

Abstract: There is a need for improved understanding on the effects of friction stir welding (FSW) on the metallurgical and mechanical properties of aluminium matrix composite (AMC). In this study, AA6092/SiC/17.5p-T6 AMC joints were produced by using FSW with varying tool rotation and traverse speeds. The microstructural characterisation by scanning electron microscopy equipped with electron backscattered diffraction (EBSD) system revealed a substantial grain refinement and a homogeneous distribution of reinforcement particles in the nugget zone. The grain size of the nugget zone was greatly influenced by weld pitch, as a key indicator to control the amount of heat input, exposure time and cooling rate. Vickers microhardness profile across the welding zone revealed a significant difference in microhardness among the base metal, heat affected zone, thermo-mechanically affected zone and nugget zone. The tensile strength of the cross-weld specimens showed a high joint efficiency of about 75% of the base metal combined with relatively high ductility. Low-cycle fatigue properties were investigated in the axial total strain-amplitude control mode (from 0.3% to 0.5%) with R = e min / e max = − 1 . The results indicate that the fatigue life of the cross-welded joints varies with grain size in the nugget zone and it is lower than that of the base metal. A significant improvement of fatigue life is found to be related to the finer equiaxed grains dominated by high angle grain boundaries in the nugget zone.

Microstructural evolution and mechanical properties of friction stir welded Mg–Zn–Y–Zr alloy

Abstract: Six millimetre thick Mg-Zn-Y-Zr plate was friction stir welded (FSW). Under a tool rotation rate of 800 rpm and a traverse speed of 100 mm/min, the defect-free weld was obtained. After FSW, coarse strip-like microstructure in forged Mg-Zn-Y-Zr alloy changed into fine equiaxed recrystallized grains in the nugget zone. Furthermore, bulky I-phase particles were broken up and dispersed with some of them being transformed to W-phase, and most of MgZn precipitates were dissolved. Micro-hardness measurement indicated that the hardness of the nugget zone was higher than that of the parent material and the lowest value of hardness was found in the heat-affected zone (HAZ). Transverse tensile tests showed that the strengths and elongation of the weld was only slightly lower than those of parent material with ultimate tensile strength of the weld reaching 95% of the parent material. (C) 2007 Elsevier B.V. All rights reserved.