Influence of Shot Peening on the Fatigue and Corrosion Behavior of the Die Cast Magnesium Alloy AZ91 hp

Author:  Muller, Rodriguez
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002036
Year of Publication:  2002
Abstract:  
Authors Clemens Muller, Roberto Rodriguez, Physikalische Metallkunde, Technische Universitat Darmstadt, Darmstadt, Germany Abstract The influence of shot peening and corrosion on the fatigue behaviour of the magnesium die cast alloy AZ91 hp is studied. Investigations on as-cast fatigue specimens show that the endurance limit is significantly reduced by the presence of pores in the near surface region. This effect can be drastically reduced by shot peening, improving the endurance limit of porous material by about 100%. The fatigue behavior of a dense material can also be improved by shot peening, but the effect is rather small (in the order of 20%). Fatigue experiments under corrosive conditions underline one of the main disadvantages of magnesium alloys, i.e. their pronounced sensitivity to contact corrosion. Iron contamination from steel shot drastically accelerates corrosion. After 3 h in a 5% NaC1 solution, corrosion attack is comparable to that observed for polished surfaces after one week. As a consequence of the accelerated corrosion, shot peening with steel shot leads to a strong deterioration of the fatigue behavior, showing clearly the need for nonferrous shot or a careful cleaning of the shot peened surface.