Zeqin Cui

Effect of environmental media on ablation rate of stainless steel under femtosecond laser multiple raster scans

We investigate the influence of environmental media on ablation rate of AISI 443 stainless steel under femtosecond (fs) laser single raster scan and multiple raster scans in air, water, and methanol. Meanwhile, the development of ablation rate with the change of fs laser-induced surface morphology in the three environmental media is comparatively studied. The results show that environmental media as well as fs laser-induced morphology control the ablation rate with the increasing number of raster scans (N). Under single raster scanning (N = 1), the ablation rate is higher in liquid than in air due to the confinement of plasma, laser-induced shockwaves, and bubble-related mechanical forces. However, under multiple raster scans, the variation in ablation rate with the increase in N in these three environmental media is complicated and is largely determined by the surface morphology induced by previous fs laser ablation. When N > 20, the ablation rate is much higher in air than in liquids due to preferential ablation caused by the formation of nanostructures-textured mound-shaped microstructures in air. Besides, the redeposition of ejected ablated materials is also an important factor that affects the ablation depth.

Laser Cladding Al-Si/Al2O3-TiO2 Composite Coatings on AZ31B Magnesium Alloy

To improve the wear resistance and corrosion resistance of magnesium alloys, a 5 kW continuous wave CO2 laser was used to investigate the laser surface cladding on AZ31B magnesium alloys with Al-Si/Al2O3 -TiO2 composite powders. A detailed microstructure, chemical composition, and phase analysis of the composite coatings were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The laser cladding shows good metallurgical bonding with the substrate. The composite coatings are composed of Mg17Al12, Al3Mg2, Mg2Si, Al2O3, and TiO2 phases. Compared to the average microhardness (50HV0.05) of the AZ31B substrate, that of the composite coatings (230HV0.05) is improved significantly. The wear resistances of the surface layers were evaluated in detail. The results demonstrate that the wear resistances of the laser surface-modified samples are considerably improved compared to the substrate. It also show that the composite coatings exhibit better corrosion resistance than that of the substrate in 3.5wt% NaCl solution.

The fabrications and optical properties of AlCrNO based Solar Selective Absorber Coatings by cathodic arc ion plating

A series of AlCrNO based solar selective absorber coatings were deposited by cathodic arc ion plating on three kinds of different infrared reflectors (AlCr, Cu, Cr) and with different deposition currents respectively. The surface morphology, phase structure and surface roughness were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and roughmeter respectively. The results show that the AlCr-AlCrNO based coating exhibited a high absorptance of 0.91 and an emittance of 0.52 when AlCr was served as infrared reflector. Meanwhile, a higher absorptance (α=0.92) of AlCr-AlCrNO based coating was obtained when varying deposition current from 50 A to 60 A. Moreover, the roughness is one of impacts on the emittance. Increasing the deposition current to 70 A brings about the raising of the roughness, increasing the emittance therefore. Keywords-solar selective absorber coating; optical properties; infrared reflectors; cathodic arc ion plating

Fatigue behavior of AZ31B magnesium alloy electron beam welded joint based on infrared thermography

Abstract Fatigue behavior of AZ31B magnesium alloy electron beam welded joint undergoing cyclic loading was investigated by infrared thermography. Temperature evolution throughout a fatigue process was presented and the mechanism of heat generation was discussed. Fatigue limit of the welded joint was predicted and the fatigue damage was also assessed based on the evolution of the temperature and hotspot zone on the specimen surface during fatigue tests. The presented results show that infrared thermography can not only quickly predict the fatigue behavior of the welded joint, but also qualitatively identify the evolution of fatigue damage in real time. It is found that the predicted fatigue limit agrees well with the conventional S–N experimental results. The evolution of the temperature and hotspot zone on the specimen surface can be an effective fatigue damage indicator for effective evaluation of magnesium alloy electron beam welded joint.