EFFECT OF SURFACE CONDITION ON FATIGUE-ST RENGTH OF DIE-CAST ALUMINUM

Surface processing like milling or shot peening involves modifications of the surface and subsurface condition of a material that can be des cribed by changes of the residual stresses, the hardness, and the surf ace roughness. Moreover, there is the possibility of introducing addit ional surface defects. In this paper the influence of these modificati ons on the fatigue behaviour of the aluminium die-casting alloy GD-AlS i8Cu3 is presented. S-N curves are determined for four surface conditi ons produced by milling, shot peening, and a combined treatment. The i mprovement of fatigue limit by shot peening is confirmed for this mate rial. The additional effect of mean stresses is determined. Investigat ions of the fatigue fracture surfaces show that pores and pipes as wel l as surface defects induced by shot peening act as fatigue crack init iation sites.