Fatigue properties of magnesium alloy AZ91 processed by severe plastic deformation. (February 2015)

• Record Type: Journal Article
• Authors: Fintová, Stanislava; Kunz, Ludvík
• Is Part Of: Journal of the mechanical behavior of biomedical materials. Volume 42(2015)
• Page Start: 219
• Page End: 228
• Publication Date: 2015-02
• Subjects: AZ91 magnesium alloy -- ECAP -- Fatigue -- Crack initiation; Biomedical materials -- Periodicals; Biomedical materials -- Mechanical properties -- Periodicals; Biomedical materials; Biomedical materials -- Mechanical properties; Periodicals; Electronic journals; 610.28
• DOI: 10.1016/j.jmbbm.2014.11.019
• Languages: English
• ISSNs: 1751-6161

Abstract

Abstract: Fatigue properties of cast AZ91 magnesium alloy processed by severe plastic deformation were investigated and compared with the properties of the initial cast state. The severe plastic deformation was carried out by equal channel angular pressing (ECAP). The ECAP treatment resulted in a bimodal structure. The bimodality consists in a coexistence of fine grained areas with higher content of Mg17 Al12 particles and areas exhibiting larger grains and lower density of Mg17 Al12 particles. Improvement of the basic mechanical properties of AZ91 (yield stress, tensile strength and ductility) by ECAP was significant. Also the improvement of the fatigue life in the low-cycle fatigue region was substantial. However the improvement of the fatigue strength in the high-cycle fatigue region was found to be negligible. The endurance limit based on 10 7 cycles for the cast alloy was 80 MPa and for the alloy processed by ECAP 85 MPa. The cyclic plastic response in both states was qualitatively similar; initial softening was followed by a long cyclic hardening. Fatigue cracks in cast alloy initiate in cyclic slip bands which were formed in areas of solid solution. In the case of severe plastic deformed material with bimodal structure two substantially different mechanisms of crack initiation were observed. Crack initiation in slip bands was a preferred process in the areas with large grains whereas the grain boundaries cracking was a characteristic mechanism in the fine grained regions.