Effects of Fine Particle Shot Peening Treatment on Fatigue Properties of Al-7Si-0.3Mg Alloy
- PDF / 3,079,300 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 57 Downloads / 217 Views
JMEPEG (2019) 28:2600–2609 https://doi.org/10.1007/s11665-019-04065-4
Effects of Fine Particle Shot Peening Treatment on Fatigue Properties of Al-7Si-0.3Mg Alloy Ming-Ze Wu, Ji-Wang Zhang, Gui-Ming Mei, Jin-Xin Zhang, and Xing Li (Submitted October 15, 2018; in revised form March 14, 2019; published online May 6, 2019) In this study, two different fine particle shot peening (FPSP) treatments were performed on Al-7Si-0.3Mg alloy specimens to evaluate their effects on fatigue properties. After the treatment, the microstructure morphology of the specimens was observed, and the surface roughness and residual stress distribution were measured. Rotating bending fatigue tests were conducted, and the fatigue fracture surfaces were observed using scanning electron microscopy (SEM). The crack initiation and propagation behavior were investigated using the replica method. The results indicate that FPSP can introduce residual stress on the surface layer of the material and refine the surface microstructure, and also change the surface roughness. At low stress amplitude levels, FPSP can improve fatigue life significantly. At 5 3 107 cycles, the fatigue strength of shot-peened specimens increased by 33% compared to unpeened specimens. In unpeened and steel shotpeened (SSP) specimens, both crystal slip and casting defects can induce fatigue failure, while only casting defects can cause failure in the case of ceramic shot-peened (CSP) specimens. Moreover, FPSP can move the crack initiation site to the subsurface from the surface. The range of threshold stress intensity factor of the material can be improved significantly by this treatment. Casting defects have a significant influence on fatigue strength; the effect on fatigue strength can be well evaluated by the modified Murakami equation. Keywords
crack initiation, fatigue strength, fine particle shot peening, residual stress, S–N curve
1. Introduction Owing to excellent mechanical and fatigue properties and corrosion resistance, Al-7Si-0.3Mg casting alloy has been widely used in the mechanical engineering field. In the highspeed railway catenary system, many supporting devices for fixing the contact lines are made of this material (Ref 1). However, fatigue failure of these supporting devices normally occurs after a long service life; such failures are harmful to the safe operation of railways (Ref 2, 3). To improve the fatigue properties of aluminum alloys, different strengthening methods are employed (Ref 4, 6-19). For the Al-7Si-0.3Mg alloy, the effects of magnesium content on fatigue properties were investigated in the previous study, and the result shows that an increase in magnesium content slows down the fatigue crack growth rate and changes the crack propagation mode from transgranular to intergranular and also improves the fatigue properties (Ref 5). Shot peening is a surface hardening treatment which involves bombarding metallic surfaces with spherical shots to introduce a residual stress layer and improve the fatigue properties. Gonza´lez et al. (Ref 4) studied the effects of
Data Loading...
