Development of mechanical properties in a CaO added AZ31 magnesium alloy processed by equal-channel angular pressing

• Published in: Materials characterization Vol. 112; pp. 105 - 112
• Main Authors: Bae, Seong-Hwan, Jung, Ki Ho, Shin, Young-Chul, Yoon, Duk Jae, Kawasaki, Megumi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2016
• Subjects: CALCIUM OXIDES; CASTING; CASTINGS; DUCTILITY; ELASTICITY; Equal channel angular pressing; GRAIN REFINEMENT; GRAIN SIZE; Magnesium; Magnesium alloy; MAGNESIUM ALLOYS; Magnesium base alloys; MATERIALS SCIENCE; Mechanical properties; Microstructure; PLASTICITY; PRECIPITATION; PRESSING; Reduction; STRAIN HARDENING; STRAINS; Strength; Ultrafine grains; YIELD STRENGTH; Ultrafine grains; Ductility; Equal-channel angular pressing; Strength; Magnesium alloy
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2015.12.009

Processing through the application of equal-channel angular pressing (ECAP) is recognized as one of the attractive severe plastic deformation techniques where the processed bulk metals generally achieve ultrafine-grained microstructure leading to improved physical characteristics and mechanical properties. Magnesium has received much attention to date for its lightweight, high strength and excellent elasticity. Mg alloys with addition of CaO is reported to provide the successful casting procedure without usage of greenhouse gas, SF6, whereas it is generally used for preventing the oxidation of Mg during casting. In the present investigation, a CaO added AZ31 (AZ31-CaO) magnesium alloy was processed by ECAP at elevated temepratures with a few steps of reduction which result in significant grain refinement to ~1.5μm after 6 passes. Compression testing at room temperature demonstrated the AZ31-CaO alloy after ECAP showed enhanced yield strength more than the as-processed commercial AZ31 alloy while both alloys maintained ductility in spite of significant reduction in grain size. The improved strength in the AZ31-CaO alloy was attributed to the formation of fine Al2Ca precipitates which experience breaking-up through ECAP and accelerate the microstructural refinement. Moreover, the preservation of ductility was attributed to the enhancement of strain hardening capability in the AZ31 alloy at room temperature. This study discusses the feasibility of using ECAP to improve both strength and ductility on magnesium alloys by applying the diagram describing the paradox of strength and ductility. •AZ31 and AZ31-CaO magnesium alloys were processed by ECAP up to 6 passes.•AZ31-CaO alloy after ECAP showed improved yield strength without losing ductility.•CaO in AZ31 forms fine Al2Ca accelerating microstructural refinement during ECAP.•Feasibility of using ECAP was shown to improve both strength and ductility in Mg.