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Abstract This paper aims to understand the impact of post-multi-pass friction stir processing (FSP) on the microstructure, mechanical, wear and fracture behaviors of the fabricated 10 cycle-accumulative roll bonded Al-2%B 4 C composites. The increase in the number of tool-passes directly improved homogeneity and fragmentation of B 4 C particles, microhardness, tensile strength (86.84–173.92 MPa) and fracture resilience of the Al-2%B 4 C composite. The tribological properties of the composite are improved with a rise in the number of tool passes. Wear rate, upper boundaries and mid-fluctuation lines of the friction coefficient decreased from 6.198 × 10−5 to 1.095 × 10−5 mm3/Nm, 0.56 to 0.19, and 0.31 to 0.11 respectively as the number of tool passes was varied between 1 and 8 passes. An increase in the sliding distance caused an overshoot of the complete waveform of friction coefficient to be above the mid-line of fluctuation due to the induced frictional/thermal input emanating from the prolonged surface-surface contact. Homogenous particle dispersion imposes abrasion wear mechanism on the composite. Ductile fracture is the predominant failure mode of the composites. Post-multi-pass friction stir processing of the accumulative roll bonded Al-2%B 4 C composite is an effective approach of achieving high performance in Al-B 4 C composite. Highlights • Multi-pass FSP on accumulative roll bonded Al-2%B 4 C composites was carried out. • Fragmentation and dispersion of B 4 C particles are enhanced by multi-pass FSP. • An inverse relationship exists between the number of FSP passes and average grain size. • Tensile strength and fracture resilience are improved by multi-pass FSP. • Wear loss, wear rate and friction coefficient are inhibited by multi-pass FSP. [ABSTRACT FROM AUTHOR]

• Diffusion brazing of IN738 to SiC ceramic was conducted using Ag-Cu-Ti interlayer. • Influence of bonding time during diffusion brazing of SiC/Ag-Cu-Ti/IN738 on metallurgical and mechanical properties was appraised. • Enhancing the bonding time also increased the shear strength of the SiC/Ag-Cu-Ti/IN738 joints by 27%. Diffusion brazing of SiC ceramic to IN738 using an Ag-Cu-Ti powder-mixture as an interlayer was carried out for the first time. The impact of the bonding time (30 and 45 min) on metallurgical features and shear strength of the joints was assessed. The results revealed that raising the bonding time resulted in expanding of the brazing layer from 46.98 µm to 55.31 µm. Besides, increasing the bonding time also enhanced the shear strength of the SiC/Ag-Cu-Ti/IN738 joints. [ABSTRACT FROM AUTHOR]

This paper examines the use of pre-fabricated interlocking arms/threading in enhancing the strength of friction stir spot welded hybrid joints of AA2219/PP-C30S polypropylene polymer by varying parameter combination. The process involves the fabrication of a pre-threaded hole on the Al alloy prior to the joining process, and the threading/crest-pitch profile aids mechanical interlocking. The peak temperature, crest-pitch interlocked profiles, microstructural and mechanical properties of the joints were examined. The results show that an increase in the tool rotational speed increases the thickness of the reaction layer (between the Al and the polymer substrates), the shear-tensile load (268–540 N), and the cross-tensile load (171–321 N) of the hybrid AA2219/PP-C30S joint. A rise in rotational speed reduces the volume of the unfilled zone while the formation of interfacial crack/discontinuity is promoted. Adhesive bonding impedes the formation of discontinuity/crack at the interface of the Al alloy and the reaction layer. The fracture of the joint is controlled by the volume of the unfilled zone, adhesively bonded region, and crest-pitch interlocked region. [ABSTRACT FROM AUTHOR]

This work investigates the microstructural features and mechanical properties of joints of low-carbon steel friction stir spot welded by changing tool rotational speed and dwell time. Microstructural evaluation, peeling, tension-shear and micro-hardness tests were employed to characterize the properties of the welded joints. The results show that an increase in the tool rotational speed promotes the formation of more weld flash, and it equally changes the flash morphology from ring flash to a combination of ring and serrated flashes. A fine immediate tool contact region is formed in the stir zone (SZ) and the width of the ITCR increases with the tool rotational speed and tensile-shear failure load. Besides the ITCR, the SZ uniquely consists of the shoulder undersurface region (SZ I) and vortex region (SZ II) with average grain sizes of about 10.9 and 16.66 µm, respectively. An increase in tool rotational speed improves the micro-hardness, and the average diameter of the weld nugget (from 4.5 to 5.5 mm). Base metal–nugget interface failure (650 rpm) and base metal necking-induced failure (1250 rpm) are the two forms of weld failure obtained in the welded samples. [ABSTRACT FROM AUTHOR]

This study examines the effect of different concentrations of Cr and Mn on the microstructure and mechanical properties of Al-10%Mg-0.1%Ti Alloy by using Al-10Cr and Al-10Mn master alloys. The microstructures were studied via the aid of an optical microscope (OM), X-ray diffraction (XRD) and energy dispersive X-ray (EDS) integrated with scanning electron microscopy (SEM). Cr and Mn contents promote the formation of Al 7 Cr and Al 11 Cr 2 , and Al 6 Mn phases in the structures of the alloy. The mechanical properties of the alloy increase with Mn content (0.5–3 wt%) due to grain refining and dispersion hardening effect of Al 6 Mn while higher Cr content precipitates deleterious secondary brittle phase of Al 11 Cr 2 . Cr and Mn contents beyond 1 and 3 wt% deteriorate the ultimate tensile strength (UTS) and percentage elongation of the as-cast alloy due to the presence of higher area fraction of brittle intermetallic phases. A direct relationship exists between hardness values and the addition of Cr and Mn contents. Low and high Cr and Mn contents show ductile and brittle fracture modes. [ABSTRACT FROM AUTHOR]

This study aims to improve the local shear behaviors of dissimilar spot welds of Al alloys through a particle-dispersion strengthening mechanism. Probe-less friction stir spot processing of the AA5083-H112 and AA5754-O alloys with B 4 C ceramic reinforcement was investigated by modifying the tool shoulder surfaces. The smooth and scrolled shoulder tools were utilized for this study. The mechanical properties of the B 4 C-reinforced spots were examined via the use of the miniaturized shear punch testing method and the tensile-shear test. At an unchanged process condition, the scrolled shoulder tool improved particle dispersion and dislocation density to an extent while it significantly reduced the average B 4 C particle size from 60 to 6.71 μm more than that of the smooth shoulder tool. The scroll-pattern-assisted straining, material flow. The wear rate was significantly reduced in the sample fabricated with the scroll tool. The scrolled shoulder tool is recommended for the fabrication of the B 4 C-reinforced spots. • The change in the tool shoulder surface has an insignificant impact on the shoulder indentation zone (SIZ). • The sample fabricated with a scrolled tool has a slightly more dislocation density due to the high straining and particle disintegration. • The scroll-pattern assisted straining, material flow and particle disintegration effects improved the shear force of the weld. • The sheared surfaces of the sample produced by scrolled tool had more elongated dimples as compared to the sample produced by the smooth tool. [ABSTRACT FROM AUTHOR]

This study investigated the influence of changes in the tool shoulder diameter on the microstructure, bonding, diffusion, and tensile-shear behaviors of the dieless friction stir rivetted CP-copper/Zn/AISI 321 stainless steel joints. The results reveal that the increase in the shoulder diameter increases the peak temperature, width of the brazed and stir zones, and the tensile-shear load (1944–2429 N) of the joints. The wider tool shoulder produced a good metallurgical/interfacial bonding at the stir zone and restrained upper sheet bulging (USB) effect at the brazed zone of the joint whereas USB-induced sheet separation and lateral unbonded path could not be prevented with the smaller tool shoulder diameter (12 mm). The change of the tool shoulder diameter changes the fracture behavior and the diffusion gradients of Cu from steep to gradual profile due to differences in the friction-induced heat input/temperature. A wider tool shoulder diameter is recommended for defect elimination and improved strength. • The influence of changes in the tool shoulder diameter on the microstructure and tensile-shear behaviors of the dieless friction stir rivetted CP-copper/Zn/AISI 321 stainless steel joints. • A larger area fraction of fine dendrites is found at the brazed zone of the sample produced with a 15 mm tool shoulder diameter. • The increase in the tool shoulder diameter improves interfacial bonding and cutback USB-induced sheet separation at the brazed zone. • A change of the tool shoulder diameter from 12 to 15 mm improved the tensile-shear load of the joint from 1944 to 2429 N due to good metallurgical bonding. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys, especially GTD-111, are widely used in the aerospace industry. Due to the high amount of Cr, the IN625 superalloy can be a good option for the surface protection of GTD-111. In this study, IN625 powder was cladded on GTD-111 using a pulsed Nd: YAG laser. This study aimed to investigate the effect of laser process parameters such as power, scan speed, and powder feed rate on microstructure development, defects, and hardness of the cladded samples. The results of this study showed that with increasing laser power from 150 to 300 W, the solidification structure tends to form equiaxed grains due to the decreasing GR from 30,751 to 20,058 °C/s and G/R from 1230to 802 °C/mm2. While at the laser power of 300 W, the tendency to form liquated cracks is increased due to the expansion of HAZ and the consequent increase in the reaction of crack-sensitive phases such as γ′, γ-γ′, and MC within the matrix. The tendency to form an equiaxed/coaxial region in the clad zone (CZ) decreased with an increase in the powder feeding rate. The inclination to form lateral porosity increased due to the reduction of the laser time interaction with the sample surface. On the other hand, by increasing the scan speed from 4 to 7 mm/s, the tendency to form cracks in the interface of the clad-substrate and HAZ increases due to the increased stresses caused by cooling. Unlike scanning speed and laser power, with increasing powder feeding rate, the distance between dendritic arms at the bottom of the coating has decreased from 1.12 to 1.02 μm. In this study, it was found that with increasing the heat input, the solidification rate decreases and as a result, more time is created for increasing the coating dilution. The distance between the dendrites subsequently increases and coarsening of carbide particles also occurs. • The effect of laser process parameters such as average power (P av), scanning speed (V), and powder feeding rate (F) on the microstructural behavior of coatings and substrates was investigated. • With distance from the coating-substrate interface, the grain structure changed from cell to column and then coaxial due to reduced G/R. • With increasing laser power, the sensitivity to liquation cracks in HAZ increased due to the presence of cracking sensing phases such as γ′ phase, γ-γ′ eutectic and MC carbide. [ABSTRACT FROM AUTHOR]

Particle strengthening of in-situ Al-Mg 2 Si composites hinges on effective geometrical parameters (size, distribution, morphology, and volume fraction) of the inherent primary Mg 2 Si particles. The use of solid-state friction stir processing (FSP) in a multi-pass mode is recognized as a secondary processing route capable of achieving desirable geometrical parameters of Mg 2 Si particles in Al-Mg 2 Si composites as compared to other routes. This paper thus studies the microstructure, mechanical properties, and tribological behavior of the multi-pass FSPed in-situ Al-25Mg 2 Si composite with a threaded triangular pin tool. The FSP was conducted at constant tool rotational and traverse speeds of 1000 rpm and 80 mm/min for 1–6 passes. The results showed a decline in the average Mg 2 Si size (115–3.25 μm), porosity content (5.8–0.14%), and primary Mg 2 Si particle-depleted region as the FSP passes are increased (0–6). Improved geometrical parameters of the primary Mg 2 Si particles enhance microhardness (178–272 HV), tensile strength (102–233 MPa) and wear resistance of the Al-25%Mg 2 Si composite via particle dispersion and dislocation strengthening effects, grain refinement, and microstructural densification. Multi-pass FSP can be adopted as a better substitute to element addition, casting modification, heat treatment and electromagnetic stirring in effectively controlling the geometrical parameters of the primary Mg 2 Si in in-situ Al-Mg 2 Si composites for improved mechanical and tribological properties. • Multi-pass FSP was applied to Al-25Mg 2 Si composite. • FSP pass number increase improved the fragmentation and redistribution of Mg 2 Si particles. • The matrix grain size reduced as the number of FSP passes increased. • Tensile strength, microhardness, and compressive strength of Al-25Mg 2 Si composite enhanced by multi-pass FSP. • Wear rate and friction coefficient of Al-25Mg 2 Si composite reduced by multi-pass FSP. [ABSTRACT FROM AUTHOR]