Study on the surface layer properties of magnesium alloys after impulse shot peening

Shot peening is a commonly used method of finishing machine elements in the manufacturing process. One variation of shot peening is the impulse shot peening. This paper presents the influence of impulse shot peening technological conditions on the surface roughness (parameters Ra and Rt), topography, and microhardness. The FEM was used to determine the S11 stresses. In the experiment and simulation tests, AZ31 and AZ91HP magnesium alloy samples were used. Variable parameters in the impulse shot peening process were impact energy E (15-185 mJ), ball diameter d (3-15 mm), and impact density j (3-44 mm-2). As a result of the tests carried out, it was found that after impulse shot peening, the surface topography is change, microirregularities are flattened, and numerous depressions are formed, which can be potential lubrication pockets. The 2D surface roughness parameters for most impulse shot peening conditions are lower than for the pre-machining. The roughness parameters for magnesium alloy AZ91HP are lower than for AZ31. This is most likely due to the lower elongation A. The microhardness after impulse shot peening increased by 20 to 87 HV. As a result of FEM of the impulse shot peening, compressive stresses S11 were created in the surface layer. The depth of occurrence of S11 stresses is from 1.5 to 3.5 mm, and their values for the AZ91HP magnesium alloy samples are 10 to 25% lower than for the AZ31 alloy samples. The most favorable results of the tested properties of the surface layer were obtained for E = 100 mJ, d = 10 mm, and j = 11 mm-2. The abstract serves both as a general introduction to the topic and as a brief, non-technical summary of the main results and their implications.