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Dejia Liu,Mingxue Shen,Yanchuan Tang,Yong Hu,Longzhi Zhao 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.5
Multipass friction stir processing (FSP) can result in a homogeneous microstructure and significant improvement in mechanicalproperties of magnesium alloys. Few studies have concentrated on the surface properties of Mg–Zn–Zr alloy duringmultipass FSP. The aim of this study was to investigate the microstructure evolutions as well as the effects on the surfacecorrosion and wear resistance of ZK60 plates during multipass FSP. An interesting finding is that FSP can significantly refinethe grains and improve the surface properties of ZK60 alloy. However, subsequent passes of FSP cannot further reduce thegrain size in the stir zone, but they cause an increase in the grain size in the ZK60 alloy. In addition, the subsequent passesof FSP are not beneficial, but rather are, harmful to the corrosion resistance of ZK60 alloy. There is little positive effect onthe improvement in the wear resistance of ZK60 plates.
Yong Hu,Fei Liu,Longzhi Zhao,Yanchuan Tang,Haitao Jiao 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.5
Al15Mg45Li39Ca0.5Si0.5 LW-HEAs with a density of 1.45 g/cm3 was designed and fabricated by magnetic suspension furnace. The non-dendritic globular microstructures of Al15Mg45Li39Ca0.5Si0.5LW-HEAs were prepared by isothermal heat treatment,and the effects of isothermal temperatures and holding times on the microstructures of semi-solid Al15Mg45Li39Ca0.5Si0.5LW-HEAs were investigated by optical microscope and scanning electron microscope. The results indicate that the phasesof Al15Mg45Li39Ca0.5Si0.5LW-HEAs consist of HCP phases and intermetallic compounds. With the increase of isothermaltemperature, the average grain size increases and the shape factor increases first and then decreases. With the prolongationof holding time, the average grain size increases first, then decreases and then increases again, and the shape factor alsoincreases first and then decreases. The semi-solid Al15Mg45Li39Ca0.5Si0.5LW-HEAs have a low coarsening coefficient. Compared with the as-cast Al15Mg45Li39Ca0.5Si0.5LW-HEAs, the ultimate strength, plasicity and hardness of smei-solidAl15Mg45Li39Ca0.5Si0.5LW-HEAs are improved by 25.7%, 18.5% and 89.7%, respectively.
Dejia Liu,Rui Guo,Yong Hu,Mingxue Shen,Yanchuan Tang,Longzhi Zhao,Deying Li,Xiangjie Wang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.6
High-entropy alloys having excellent properties are particularly suitable for the application as the filler metals in welding. In the present study, multi-component mixed powders of FeCoCrNiMn and CrFeNi2.4Al0.6,based on a high-entropy design,as well as the comparative 316L stainless steel powders, were used as the filler metals, to achieve the dissimilar weldingbetween 304 stainless steel and SMA490BW steel by laser deposition welding. By comparative analysis of the microstructureand mechanical properties of three types of joints, the feasibility and weld-ability of the filler metal powders based on ahigh-entropy design were studied. It was found that the melting of base metal (BM) and weld metal dilution had an impacton the set high-entropy component in the weld zone. And high-entropy structures were achieved in the weld zone by usingthe powders of CrFeNi2.4Al0.6. Compared to the BM of SMA490BW steel, three types of joints presented a higher notchedtensile strength and had a better corrosion resistance. The joint welded using the powders of CrFeNi2.4Al0.6had the lowesthardness value in the weld zone, in which the joint was fractured during the notched tensile tests. The other two jointsfractured near the notch in the SMA490BW steel side. Transgranular fracture and a typical dimple fracture were observedin the fractured joints.