Effect of ultrasonic surface rolling processing on surface integrity and mechanical properties of ZL205A alloy

This study investigates the effects of ultrasonic surface rolling process (USRP) parameters—static pressure, feed speed, ultrasonic amplitude, and rolling passes—on the surface integrity, mechanical properties, and microstructural evolution of T6 heat-treated ZL205A Al–Cu alloy. Comprehensive characterization demonstrates that USRP treatment significantly enhances surface quality, producing an ultra-smooth surface with a minimum roughness (Ra) of 0.08 μm while simultaneously increasing surface microhardness to 168.10 HV and introducing compressive residual stresses of −128.3 MPa. Empirical models were established to correlate microhardness and surface roughness with USRP processing parameters. Microstructural analysis reveals that USRP generates a gradient nanostructured surface layer with grain refinement to ∼157.2 nm and an elevated dislocation density of 6.90 × 10¹⁴m⁻². Quantitative analysis shows that the enhancements in both microhardness and yield strength follow a linear relationship with the square root of dislocation density, confirming dislocation strengthening as the dominant mechanism for the observed mechanical property improvements.