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Friction-Stir Processing (FSP) was applied on AA1050 Aluminum Alloy (AA) to find the highest mechanical properties among 28 combinations of the rotational and traverse speed (800-2000 rpm and 50-200 mm.min-1) and four different tool probe shapes (threaded, columnar, square and triangle). To this aim, the AA standard sheet went through a single pass of FSP. The 1600 rpm and 100 mm.min-1 with threaded tool probe was chosen as the best combination of rotational and traverse speed. Grain size at the Stirred Zone (SZ) was studied using Optical Microscopy (OM). The results showed that the SZ S grain size was refined from 30 gm down to about 12 gm due to dynamic recrystallization during FSP. The processed sample exhibited improved hardness, yield stress, ultimate tensile strength, elongation up to 65, 80, 66, and 14%, respectively, compared to the annealed AA sample. Studying fractographic features by OM and field emission scanning electron microscope (FESEM) revealed a dominantly ductile fracture behavior. [ABSTRACT FROM AUTHOR]

The heat‐affected zone (HAZ) softening is considered one of the most significant challenges during welding of ferrite–martensite dual‐phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir‐welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly reduces the weld temperature. It is also observed that the thermal diffusivity of the BP has a substantial effect on the microstructure development and mechanical properties of the welded joint. Increasing the thermal diffusivity of the BP results in a reduction of HAZ softening from 20 to 7 HV and improving tensile strength and total elongation of the joint by 40 MPa and 6.2%, respectively. Work hardening behavior and absorbed energy before the fracture are significantly improved by the replacement of steel BP with a copper. [ABSTRACT FROM AUTHOR]

Production of Al1050/TiO2-graphite hybrid nanocomposite via friction stir processing (FSP) was studied. The effect of graphite-to-TiO2 volume fraction ratio (Gr/TiO2), at a constant rotational speed (ω) and three levels of tool traverse speed (ν), on the microstructural evolution and mechanical properties of the nanocomposites was investigated. While TiO2 is supposed to enhance the strength and hardness, graphite is believed to improve the tribological behavior. Furthermore, formation of intermetallic compounds (IMCs) through the solid-state reactions between the reinforcements and aluminum matrix may also promote the mechanical properties. To assess these assumptions, longitudinal and transverse tensile strength, Vickers microhardness, and pin-on-disk wear tests were performed. Microstructural changes and formation of compounds were explored using optical microscopy and field-emission–scanning electron microscopy (FE-SEM) as well as X-ray diffraction (XRD). ω/ν and Gr/TiO2 ratios were introduced as the main parameters to obtain the desirable material flow and particle distribution. The hardness of the nanocomposites increased by superior distribution of the reinforcements throughout the matrix. The yield strength of the nanocomposites increased up to ~82 and ~50 pct compared to the as-received and friction-stir-processed Al1050 with no reinforcement, respectively. The tribological behavior of nanocomposites improved by the presence of the graphite acting as a solid lubricant on the sliding surface. [ABSTRACT FROM AUTHOR]