The effects of cold deformation and low temperature aging on the microstructural stability of a peak aged (PA) Al 6061 alloy were investigated by means of DSC and microhardness measurements. During aging at a relatively low temperature (100 °C) of the PA material, a small increasing of the mechanical properties was detected, which was explained by the formation of atomic clusters, GP zones and β phase. The response to the aging treatment of the cold deformed materials depends on both the level of the cold deformation and the aging temperature. During aging at relatively low temperature (100 °C), in contrast to the 75 % deformed material that shows a small variation in their mechanical properties, the mechanical properties, of the 30 % deformed material, are almost constant. This was attributed to the higher driving force of the recovery reaction in the heavily deformed material. In the other hand, aging at relatively higher temperature (140 °C) of the heavily deformed material, leads to a fast softening due to an increasing of the recovery kinetics.
The present study investigates the metallurgical behavior of direct-drive friction-welded (DDFW) joints for high Cr, Ni, and Mo steel (AISI 316). Macro-microscopic, microhardness, and X-ray diffraction (XRD) were conducted. The results for the macroscopic view showed that the narrow welding center did not exceed 600 µm and there were no macro cracks or defects, indicating a uniform structure. The microstructure exhibited a significant welded joint interface with microcavities and a grain refinement of 10 µm, about three times smaller than the grain size of AISI 316, due to the creation of a highly plastically deformed zone (HPDZ), while the thermo-mechanically affected zone (TMAZ) formed in the neighboring area with a grain growth of about 100 µm, relatively enlarged three times compared to AISI 316 and time time related HPDZ. Thus, the high level of microhardness was investigated at the welding center and low values in the neighboring area were caused by the formation of the HPDZ and TMAZ, respectively. XRD also illustrated the concentration of gamma iron at the 111 level due to the grain refinement resulting from high plastic deformation.
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