Microstructural and mechanical properties of dissimilar aluminum alloys/Al₂O₃ nanocomposite joint via friction stir welding

152-158In this study, AA5083-H116 and AA7075-T6 aluminum alloys are joined by friction stir welding (FSW) and incorporating alumina nanoparticles into the joint to produce an aluminum alloys/Al2O3 nanocomposite. The joining process is carried out by using a square pin profile tool at rotational and traverse speeds of 800 rpm and 50 mm/min, respectively. Microstructural investigation by scanning electron microscopy (SEM) and optical microscopy (OM) are revealed a clustered structure that consists of Al2O3-rich and Al2O3-free areas in the stir zone (SZ). Besides, it is observed that the grain size of the joint is reduced after addition of nanoparticles. Moreover, owing to the presence of Al2O3 nanoparticles, the resultant hardness profile shows the superior hardness of the reinforcement-included specimen, while the ultimate tensile strength and percentage of elongation are reduced

Formation And Distribution of Brittle Structures in Friction Stir Welding of AA 6061 To Copper. Influence of Preheat

International audienceIn this paper, apart from introducing brand – new warm friction stir welding (WFSW) method, the effect of preheating on friction stir welded of copper and aluminum alloys sheets and its influence on improving the mechanical properties of the weld were investigated. Sheets of aluminum alloy 6061 and copper with thickness of 5mm were used. The tool was made of tool steel of grade H13 with a threaded cone shape. Rotational speeds (w) of 1200-1400 rpm and traverse speeds (v) of 50-100 mm/min were used for better understanding the behavior of the tools during the heat input. The sheets were kept in furnace with temperature of 75C and 125˚C and welding was done afterwards. At last, tensile and micro hardness tests were done to compare the mechanical properties of the welds. Considering to the high thermal conductivity of both copper and aluminum, the reason of increase in strength of the joints could be related to the low temperature gradient between the weld zone and base metal because the heat gets out of the stir zone with lower steep. A significant increase in hardness is observed in the SZ for the following reasons: (i) the presence of concentric grains with intensely refined recrystallization and (ii) the presence of intermetallic compounds. The tensile test results showed 85% increase in the strength of preheated joints. The maximum strength occurs for preheating of 75˚C, rotational speed of 1200 rpm and traverse speed of 50 mm/min. In the present study, intermetallic compounds and the precipitates are moved to the grain boundaries during the welding process. These precipitates act as strong obstacles to the movements of dislocations and increase the deformation resistance of material. This phenomenon may result in locking of grain boundaries and consequently decrease of grain size. This grain refinement can improve the mechanical properties of welds. Accordingly, hardness and strength of the material will be increased

Investigation of the effect of Al-8B master alloy and strain-induced melt activation process on dry sliding wear behavior of an Al–Zn–Mg–Cu alloy

Abstract This study was undertaken to investigate the influence of Al–8B master alloy and modified strain-induced melt activation process on the structural characteristics and dry sliding wear behavior of Al–12Zn–3Mg–2.5Cu aluminum alloy. The optimum amount of B containing master alloy for proper grain refining was selected as 3.75wt.%. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The optimum temperature and time in strain-induced melt activation process are 590°C and 10min, respectively. T6 heat treatment was applied for all specimens before wear testing. Significant improvements in wear properties were obtained with the addition of grain refiner combined with T6 heat treatment. Dry sliding wear performance of the alloy was examined in normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3Mg–2.5Cu aluminum alloy to the dry sliding wear. The results showed that dry sliding wear performance of globular microstructure specimens was a lower value than that of B-refined specimens without strain-induced melt activation process.University of Tehra