Xiaomi Chen

In this study, a scalable surface modification strategy for M2 high-speed steel was applied using multiple-pass friction stir processing (FSP) with overlapping ratios of 25%, 50%, and 75%. A comprehensive investigation of the microstructure, surface hardness, wear, and corrosion resistance was conducted to elucidate the properties of FSPed M2 as a function of the overlapping ratio. In the single-pass FSPed M2, the major phase was martensite and the minor phases included retained austenite where refined carbides (M₆C, M₂₃C₆, and MC) were detected. However, back-tempering occurred near the overlapped zone (OZ) between consecutive tracks for the multiple-pass FSPed M2. The martensite formed in the first pass was turned into tempered martensite by the thermal cycle from the subsequent pass. This back-tempering resulted in a localized decline in hardness from 900 to 650 HV_0.2. Further wear tests revealed that the wear rates of the tempered zone (TZ) of the multiple-pass FSPed M2 (FSP25%: 1.40 × 10⁻⁵ mm³/N·m, FSP50%: 1.20 × 10⁻⁵ mm³/N·m and FSP75%: 1.00 × 10⁻⁵ mm³/N·m) are all higher than that of SZ of the single-pass FSPed M2 (0.75 × 10⁻⁵ mm³/N·m), indicating lower wear resistance of the TZ. Moreover, increased carbide content in the TZ led to the depletion of passivating elements near proximity of the tempered martensite, acting as the active sites for selective corrosion attack. The corrosion potential (E_corr) and corrosion current density (I_corr) increased significantly, with values of −397.6 ± 5.6 mV and 9.5 ± 0.8 μA·cm⁻² for FSP25%, −424.4 ± 6.0 mV and 14.7 ± 1.7 μA·cm⁻² for FSP50%, and −440.9 ± 2.8 mV and 17.1 ± 1.9 μA·cm⁻² for FSP75%.

With the ongoing development of lightweight automobiles, research on new aluminum alloys and welding technology has gained significant attention. Friction stir welding (FSW) is a solid-state joining technique for welding aluminum alloys without melting. In this study, novel squeeze-cast Al-Si-Mg-Fe-Zn alloys with different Zn contents (0, 3.4, 6.5, and 8.3 wt%) were friction stir welded (FSWed) at a translational speed of 200 mm/min and a rotational speed of 800 rpm. These parameters were chosen based on the observations of visually sound welds, defect-free and fine-grained microstructures, homogeneous secondary phase distribution, and low roughness. Zn can affect the microstructure of Al-Si-Mg-Fe-Zn alloys, including the grain size and the content of secondary phases, leading to different mechanical and corrosion behavior. Adding different Zn contents with Mg forms the various amount of MgZn₂, which has a significant strengthening effect on the alloys. Softening observed in the weld zones of the alloys with 0, 3.4, and 6.5 wt% Zn is primarily attributed to the reduction in Kernel Average Misorientation (KAM) and a decrease in the Si phase and MgZn₂. Consequently, the mechanical strengths of the FSWed joints are lower as compared to the base material. Conversely, the FSWed alloy with 8.3 wt% Zn exhibited enhanced mechanical properties, with hardness of 116.3 HV_0.2, yield strength (YS) of 184.4 MPa, ultimate tensile strength (UTS) of 226.9 MP, percent elongation (EL%) of 1.78%, and a strength coefficient exceeding 100%, indicating that the joint retains the strength of the as-cast one, due to refined grains and more uniformly dispersed secondary phases. The highest corrosion resistance of the FSWed alloy with 6.5%Zn is due to the smallest grain size and KAM, without MgZn₂ and the highest percentage of {111} texture (24.8%).

In this study, friction stir processing (FSP) was employed to enhance the corrosion properties through local modification of the microstructure of AlSi10Mg alloy fabricated by laser-powder bed fusion (L-PBF) technology. Different combinations of processing parameters were tested, with rotation speeds ranging from 800 to 1600 rpm and traverse speeds from 100 to 300 mm/min, in order to evaluate the impact of traverse speed on the mechanical and electrochemical properties of L-PBF AlSi10Mg. The results showed that FSP under the different processing parameters had effectively transformed the coarse grain structure of the as-built AlSi10Mg into fine and equiaxed grain structures in the stir zone, while also causing fragmentation and refinement of the Si networks within the material. The hardness of the stir region decreased compared to the as-built material, without significant influence from the processing parameters. However, the Si content within the stir zone is dependent on the combined influence of the rotation and traverse speeds, which in turn, affected the corrosion resistance of the material, with a lower traverse speed promoting a higher Si concentration in the Al-matrix, improving the corrosion performance of the processed material.

In this study, the effects of friction stir processing (FSP) parameters on the microstructure and hardness of cast Al-Si-Fe-Mg alloy were investigated. Orthogonal arrays were applied in the design of the experiments. The selected parameters for the experiments included rotation speed, transverse speed, penetration depth, and tilt angle. The microstructure and hardness of the FSPed Al-Si-Fe-Mg were studied using optical and scanning electron microscopy, and microhardness testing, respectively. The quadratic model was proposed to fit the experimental data of hardness. Signal-to-noise ratio (S/N) analysis showed the maximum hardness achieved when rotation speed, transverse speed, penetration depth, and tilt angle were chosen as 1600 rpm, 400 mm/min, 0.1 mm, and 1.5°, respectively. Taguchi’s analysis of variance (ANOVA) was used to determine the significant FSP parameters on hardness, which revealed that rotation speed was the most dominant processing parameter, followed by transverse speed, tilt angle, and penetration depth. Moreover, a quadratic polynomial model was developed to predict and optimize the combination of the parameters, enabling superior mechanical properties. Subsequently, the verification of the microstructure was conducted, demonstrating good agreement between the experimental observation of the microstructure and estimated outcomes.