Surface nanocrystallization treatment of AZ91D magnesium alloy by cold spraying shot peening process

• Published in: Surface & coatings technology 2019-09, Vol.374, p.485-492
• Main Authors: Wang, Hong-Tao, Yao, Hai-Long, Zhang, Meng-Xian, Bai, Xiao-Bo, Yi, Zhi-Hai, Chen, Qing-Yu, Ji, Gang-Chang
• Format: Article
• Language: English
• Subjects: AZ91D alloy; Coefficient of friction; Cold spraying; Cold spraying shot peening (CS-SP); Deformation; Frictional wear; Grain size; Magnesium alloys; Magnesium base alloys; Microhardness; Microscopy; Microstructure; Nanocrystals; Optical microscopy; Properties; Shot peening; Sliding friction; Surface nanocrystallization; Thickness; Wear resistance
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.04.093

In this paper, a new cold spraying shot peening (CS-SP) technology was used to produce surface nanocrystallization (SNC) of AZ91D magnesium alloy for the first time. The structure characteristics of SNC layer on AZ91D alloy were investigated by means of X-ray diffractometer (XRD), optical microscopy (OM), scanning electronic microscopy (SEM) and transmission electron microscopy (TEM), respectively. The microhardness distribution of AZ91D specimen after CS-SP treatment was tested by a microhardness tester. The wear property and the coefficient of friction (COF) of AZ91D alloy before and after CS-SP treatment were investigated using the sliding wear tester. Experimental results showed that SNC layer with thickness about 40 μm can be prepared on AZ91D alloy by the CS-SP process. The average grain size of SNC layer was in range of 50–80 nm and a large number of deformation twin bands existed beneath the nanocrystalline layer. The microhardness of AZ91D specimen after CS-SP treatment exhibited a gradient distribution with the depth and the microhardness value of the outermost layer was up to 160 Hv0.025 about twice as that of the matrix. In comparison with the untreated one, the AZ91D alloy after CS-SP treatment showed the lower COF and the enhanced wear resistance. •Surface nanocrystallization of AZ91D alloy was induced by cold spray shot peening.•The hardened layer consisted of nanograin region and deformation twin bands region.•The average grain size of nanograin region was in a range of 50–80 nm.•The microhardness variation of harden layer in the depth showed a gradient decrease.•The treated AZ91D alloy exhibited the improved mechanical properties.