Evolution of microstructure and crystallographic texture during dissimilar friction stir welding of duplex stainless steel to low carbon-manganese structural steel

Electron backscattered diffraction (EBSD) was used to analyze the evolution of microstructure and crystallographic texture during friction stir welding of dissimilar type 2205 duplex stainless steel (DSS) to type S275 low carbon-manganese structural steel. The results of microstructural analyses show that the temperature in the center of stirred zone reached temperatures between Ac 1 and Ac 3 during welding, resulting in a minor ferrite-to-austenite phase transformation in the S275 steel, and no changes in the fractions of ferrite and austenite in the DSS. Temperatures in the thermomechanically affected and shoulder-affected zones of both materials, in particular toward the root of the weld, did not exceed the Ac 1 of S275 steel. The shear generated by the friction between the material and the rotating probe occurred in austenitic/ferritic phase field of the S275 and DSS. In the former, the transformed austenite regions of the microstructure were transformed to acicular ferrite, on cooling, while the dual-phase austenitic/ferritic structure of the latter was retained. Studying the development of crystallographic textures with regard to shear flow lines generated by the probe tool showed the dominance of simple shear components across the whole weld in both materials. The ferrite texture in S275 steel was dominated by D 1, D 2, E, E¯ , and F, where the fraction of acicular ferrite formed on cooling showed a negligible deviation from the texture for the ideal shear texture components of bcc metals. The ferrite texture in DSS was dominated by D 1, D 2, I, I¯ , and F, and that of austenite was dominated by the A, A¯ , B, and B¯ of the ideal shear texture components for bcc and fcc metals, respectively. While D 1, D 2, and F components of the ideal shear texture are common between the ferrite in S275 steel and that of dual-phase DSS, the preferential partitioning of strain into the ferrite phase of DSS led to the development of I and I¯ components in DSS, as opposed to E and E¯ in the S275 steel. The formations of fine and ultrafine equiaxed grains were observed in different regions of both materials that are believed to be due to strain-induced continuous dynamic recrystallization (CDRX) in ferrite of both DSS and S275 steel, and discontinuous dynamic recrystallization (DDRX) in austenite phase of DSS

The microstructural evolution of friction stir welded AA6082-T6 aluminum alloy during cyclic deformation

The fatigue behavior of a thick section friction stir welded AA6082-T6 aluminum alloy was studied to compare damage mechanisms in the weld zone and the base metal. Fully reversed tension-compression strain-controlled fatigue tests were conducted to determine the cyclic stress response and stored energy to failure. Microstructure evolution during cyclic straining was followed using secondary electron imaging and electron backscatter diffraction in a scanning electron microscope. Fatigue cracking along grain boundaries and the formation of slip bands were observed to be the fatigue-induced microstructural features in the friction-stir-welded structure. In the base metal, micron-sized particles led to particle-induced cracking

Microstructure, Hardness and Impact Toughness of Heat-Treated Nanodispersed Surface and Friction Stir-Processed Aluminum Alloy AA7075

Friction stir processing (FSP) is a recent surface engineering processing technique that is gaining wide recognition for manufacturing nanodispersed surface composites, which are of high specific strength, hardness and resistance to wear and corrosion. Herein, four-pass FSP was applied on aluminum alloy 7075 (AA7075-O) with and without the addition of alumina nanoparticles (Al2O3) of average size ~40\ua0nm. All FSP parameters were constant at 40\ua0mm/min transverse speed, 500\ua0rpm and tilt angle of 3\ub0. FSP rotation direction was reversed every other pass. The friction stir-processed materials were sectioned and solution treated at 515\ua0\ub0C for 1.5\ua0h, followed by age hardening at 120\ua0\ub0C for 12, 24, 36, 48 and 60\ua0h. The effect of heat treatment regimes on microstructure, hardness and toughness was examined, as well as the fracture mode. The new friction stir-processed surfaces without and with nanodispersion showed enhancement in the hardness of the surface of the AA7075-O material (65\ua0HV) to almost a double (100 and 140\ua0HV) after four-pass FSP (before heat treatment) without and with incorporating nanoalumina particles, respectively. After 48-h aging at 120\ua0\ub0C, a significant enhancement in impact toughness was achieved for both the friction stir-processed without and with nanodispersion (181 and 134\ua0J, respectively), compared to the reference material AA7075 in T6 condition (104\ua0J)

Effect of FSP parameters and tool geometry on microstructure, hardness, and wear properties of AA7075 with and without reinforcing B4C ceramic particles

The aim of this work is to produce a surface composite by incorporating B 4 C particles on the surface of AA7075 alloy through friction stir processing (FSP) using both a pinless and a cone pin tool. The influence of friction stir processing parameters on the microstructure, hardness, and wear properties of the processed surface composites was investigated. The studied parameters include rotational tool speed (400 and 600 rpm) and number of passes (1, 2, 3, and 4 passes). Microstructural analysis and microhardness profiles were performed on cross sections of FSPed samples at different depths. Wear behavior of the processed samples was evaluated by means of dry sliding tests. The results indicate that (i) increasing the number of passes results in improving the distribution of B 4 C reinforcing particles, (ii) samples processed with the pinless tool displayed a more homogeneous distribution of the reinforcement in the outer layer of the material with respect to the samples processed with the cone pin, (iii) the addition of B 4 C particles improved the wear resistance of the AA7075 alloy even if it led to a raise in the coefficient of friction

Influence of Friction Stir Processing on the Microstructure and Mechanical Properties of a compocast AA2024-Al2O3 nanocomposite

The effect of friction stir processing (FSP) on the microstructure and mechanical properties of a semi-solid cast AA2024-1wt.%Al2O3 nanocomposite was investigated. For comparison, plates of unreinforced AA2024 alloy were also cast and processed at the same FSP conditions (400 rpm, 20mm/min). The microstructure of all the produced materials was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Microhardness and tensile tests were carried out on the unreinforced AA2024 alloy and AA2024-Al2O3 nanocomposite before and after FSP. The addition of 1wt% of Al2O3 nanoparticles significantly reduced the grain size of both the cast and FSPed microstructures, leading to a grain size reduction from 28 \ub5m to 18 \ub5m in the cast condition, and from 3.7 \ub5m to 2.7 \ub5m after FSP. The application of FSP to AA2024-Al2O3 nanocomposite enhanced the tensile strength and yield strength by 71% and 30%, respectively, in comparison to the as cast matrix, as a result of the uniform distribution of Al2O3 reinforcement and grain refinement of Al matrix. The combined application of compocasting and FSP resulted to be a promising method to treat casting defects and to produce nanocomposites characterised by good reinforcement dispersion and high strength and ductility

Production of AlSi12CuNiMg/Al2O3 Micro/Nanodispersed Surface Composites Using Friction Stir Processing for Automotive Applications

The service life of automotive components often depends on their surface properties. Consequently, improved surface properties with the retainment of bulk characteristics are necessary for such components to guarantee enhanced mechanical and tribological properties. In this research, friction stir processing (FSP) is used to produce surface composites characterized by extruded AlSi12CuNiMg matrix and micro and nano-sized Al2O3 particles as reinforcing phase. Multiple passes of FSP using two different strategies were applied to distribute the Al2 O3 particles. The effect of the different FSP parameters and sequence of rotation direction for the applied passes was investigated. The processed surface layers were analyzed through optical and scanning electron microscopy, hardness, and wear testing. The properties of the processed composite surface showed to be affected by both the size of reinforcing particles and the processing direction sequence. A comparison between properties of the produced surface composites and the base metal was also carried out. Bench-type test developed to measure the weight loss of samples under sand erosion conditions