Xiaopei Li

Effects of electropulsing assisted ultrasonic impact treatment on welded components

Abstract The effect of electropulsing assisted ultrasonic impact treatment (EUIT) on the mechanical properties and microstructure evolution of S50C steel welded components has been investigated. The present paper presents the application of a relatively new post-weld treatment method to eliminate the residual stress and improve the surface mechanical properties. The results show that EUIT exhibits better surface modification capability than does conventional ultrasonic impact treatment. After EUIT, plastic deformation layer with strengthened grains formed on the sample surface, and residual tensile stress was converted into residual compressive stress.

Improvement of surface properties of 2316 stainless steel with ultrasonic electric surface modification

Abstract An ultrasonic electric surface modification treatment was employed to improve the surface properties of 2316 stainless steel. The surface properties of the specimens after conventional cutting, ultrasonic surface modification treatment and ultrasonic electric surface modification treatment were characterised respectively. A grain refinement layer was formed on the specimens surface after ultrasonic electric surface modification treatment. The average grain size on the top surface was refined into the submicrometre or nanometre scale. This is caused mainly by two aspects: one is the accumulation of initial tiny particles during deformation, and the other is that the ferrite is smashed into pieces due to microfatigue damage. Moreover, it was found out that the specimen after ultrasonic electric surface modification treatment at four times had shown the optimal surface properties.

Mg–3Al–1Zn alloy strips processed by electroplastic differential speed rolling

The effect of reduction per pass on the mechanical properties, microstructure and texture evolution of Mg–3Al–1Zn magnesium alloy strips processed by electroplastic differential speed rolling has been investigated. With increasing reduction per pass, the mechanical properties of the rolled strips increase. Both the shear effect and the current pulses play an important part in modifying the microstructure and texture by promoting dynamic recrystallisation. During dynamic recrystallisation, nucleus tends to nucleate in the vicinity of the shear bands. And as the progress of dynamic recrystallisation, shear bands are gradually consumed by the newly nucleated grains and become nearly indistinguishable. The athermal effect of current pulses plays an important role in promoting dynamic recrystallisation.

Texture modification of magnesium alloys during electropulse treatment

ABSTRACT Differential speed rolling (DSR) at room temperature has been carried out on two Mg–1Gd and Mg–1Zn–1Gd rare-earth-containing magnesium alloys with different thickness reductions. The cold-rolled samples were selected to investigate the microstructure and texture evolution during the electropulse treatment (EPT). Both grain refinement and texture modification have been achieved for the three cold-rolled samples, which were accompanied by nucleation and nuclei growth during EPT. The recrystallisation process could be attributed to enhanced climb activity of dislocations by EPT, which produces not only a thermal effect but also an athermal effect. Compared with Mg–1Gd, Mg–1Zn–1Gd shows a smaller recrystallisation rate, which should be related to the solute segregation and could be one of the reasons for the texture modification of the alloy. This paper is part of a themed issue on Materials in External Fields.

Fabrication of a Gradient Nano-/Micro-structured Surface Layer on an Al–Si Casting Alloy by Means of Ultrasonic–Electropulsing Coupling Rolling Process

By using a novel surface modification technique named ultrasonic–electropulsing coupling rolling (UECR) process on an Al–Si casting alloy rod, the surface of material was smoothened significantly. Meanwhile, a strengthened layer with a gradient change in hardness was obtained in the outer surface, corresponding to a homogeneous gradient nano-/micro-structure. The thickness of nanometer-thick laminated structures was at least 40xa0μm, which was much thicker than conventional ultrasonic rolling process. During UECR, the formation of the well-defined nanocrystalline structure was attributed to the high strain rate and simultaneous annealing process realized by ultrasonic impact and electropulsing treatment.

A Comparative Study on the Static Recrystallization Behavior of Cold-Rolled Mg-3Al-1Zn Alloy Stimulated by Electropulse Treatment and Conventional Heat Treatment

Cold-rolled AZ31 Mg alloy strips, with a reduction of 33xa0pct, were subjected to electropulse treatment (EPT) and conventional heat treatment (HT) to evaluate the respective influences of electropulses and temperature on the recrystallization behavior of AZ31. The highest measured temperature during the EPT (543xa0K) was used in HT. The electron backscattered diffraction results demonstrated that the EPT-stimulated recrystallization was completed within 8xa0seconds, whereas for HT, recrystallization was still far from completion even after 240xa0seconds. It was found that both the nucleation and grain growth of these two processes were totally different. In the EPT samples, nucleation tended to occur preferentially near extension twin boundaries and grain boundaries by continuous recrystallization, whereas in the HT samples, nucleation occurred mainly by grain boundaries bulging via discontinuous recrystallization. As grain growth proceeded, the texture intensities of the EPT samples decreased gradually and finally evolved into an obvious transverse-direction-split texture. This is likely attributable to the impact of electropulses on the boundary energy and the contribution of nonbasal dislocations; however, the basal-type textures of the HT samples were notably strengthened, which is associated with a 30xa0deg〈0001〉 orientation with respect to the deformed texture.

Enhanced Surface Mechanical Properties and Microstructure Evolution of Commercial Pure Titanium Under Electropulsing-Assisted Ultrasonic Surface Rolling Process

The effects of electropulsing-assisted ultrasonic surface rolling process on surface mechanical properties and microstructure evolution of commercial pure titanium were investigated. It was found that the surface mechanical properties were significantly enhanced compared to traditional ultrasonic surface rolling process (USRP), leading to smaller surface roughness and smoother morphology with fewer cracks and defects. Moreover, surface strengthened layer was remarkably enhanced with deeper severe plastic deformation layer and higher surface hardness. Remarkable enhancements of surface mechanical properties may be related to the gradient refined microstructure, the enhanced severe plastic deformation layer and the accelerated formation of sub-boundaries and twins induced by coupling effects of USRP and electropulsing. The primary intrinsic reasons for these improvements may be attributed to the thermal and athermal effects caused by electropulsing treatment, which would accelerate dislocation mobility and atom diffusion.