Search

• Prior shot peening improves the CF limit of AO coated aluminum alloy by 50 %. • AO specimens exhibit different CF failure modes under low and high applied stress. • Substrate residual stress and microstructure affect the CF crack propagating path. • Substrate residual stress relaxes in distinct mode under low and high applied stress. Plain (anodic oxidation) and composite (prior shot peening + anodic oxidation) coatings were prepared to investigate their effects on the corrosion-fatigue (CF) property of 6082-T6 aluminium alloy in a 3.5 wt% NaCl aqueous solution. The results indicate that plain coated specimens exhibited similar CF properties to as-machined specimens at low applied stresses. However, under high applied stresses, the plain coating led to a preferential fracture and was unable to effectively prevent corrosion medium. Hence, the CF property of plain coated specimens was found to be inferior to as-machined specimens at high applied stresses. The synergetic effect of substrate residual stress and microstructure beneath the coating-substrate interface reduced the crack propagating rate in the initial stage by deflecting the crack at the grain boundary. Therefore, the CF property of composite coated specimens improved as a whole when compared with as-machined and plain coated specimens. Besides, under low applied stresses, the near-interface substrate residual stress of composite coated specimens occurred the relaxation due to the substrate crack propagation, while under high applied stresses, this was due to the synergetic effect of materials' local cyclic yield and plastic flow, as well as the substrate crack propagation. [ABSTRACT FROM AUTHOR]

• The surface properties of EA4T axle steel treated by ultrasonic surface rolling process (USRP) are investigated. • Effect of USRP on the electrochemical corrosion resistance and corrosion fatigue performance is elucidated. • Residual stress relaxation mechanism of USRP-treated EA4T axle steel in air and corrosion is revealed. • Influence of residual stress relaxation on the corrosion fatigue resistance is clarified. The fatigue properties and residual stress relaxation behavior of EA4T axle steel treated by ultrasonic surface rolling process (USRP) are investigated in air and corrosive environments. The result reveals that the surface roughness (Ra) is decreased from 1.42 to 0.17 μm after the USRP. A surface layer with ultrafine grains, work hardening, and compressive residual stress (CRS) is achieved by the USRP. Compared with the as-machined specimens, the USRP specimens exhibit slightly lower electrochemical corrosion resistance but superior fatigue performance in air and corrosive environments. The dislocation density is significantly decreased in the corrosive environment during fatigue loads, accompanied by a rapid relaxation of surface CRS. The influence of USRP on the corrosion fatigue performance is elucidated. The residual stress relaxation mechanism and its influence on fatigue resistance are also analyzed. [ABSTRACT FROM AUTHOR]

In this study, EA4T axle steel specimens were subjected to three shot peening treatments: conventional shot peening (CSP), micro-shot peening (MSP) and their combination, i.e. dual shot peening (DSP). The residual stress, surface roughness, morphology, microhardness, were used to characterize the affected surface layer. The results indicated that MSP achieved maximum surface compressive residual stress (SCRS), minimum surface roughness, high surface microhardness. Moreover, compared to CSP, DSP improved the SCRS and microhardness while reducing surface roughness. However, scanning electron microscopy (SEM) observations indicated the presence of intensive defects of the DSP-treated specimens, which hindered the fatigue strength of the specimens. Fatigue tests were conducted to evaluate the effect of different treatments on fatigue life, the median S - N curve demonstrated that the fatigue limit at 107 cycles was improved by 24, 32, and 27% for the CSP, MSP, and DSP specimens, respectively. Furthermore, SEM observation was conducted to analyze the fracture mechanisms, the results indicated that the failure of all specimens originated at the surface and the fracture mechanisms were not changed by the shot peening treatments. The SCRS during the cyclic loading have also been analyzed. Moreover, the factors influencing fatigue limit improvement were discussed. [ABSTRACT FROM AUTHOR]