Design of Mg-6wt%Al alloy with high toughness and corrosion resistance prepared by mechanical alloying and spark plasma sintering

Abstract

Microstructural optimization was performed on Mg alloy produced by high-energy milling and spark plasma sintering (SPS) through systematic investigation of mechanical properties and corrosion resistance. The SPS Mg alloys degassed under low vacuum condition led to continuous and thick magnesium oxide stringer consisted of MgO crystals at particle boundary even at high sintering pressure of 130Mpa. Simultaneously, large and irregularly shaped oxide particles at grain boundary and grain inside was identified from TEM observation. Meanwhile, for fully degassed at high vacuum and SPS Mg samples, particle boundaries were discontinuous and the cuboidal MgO particles were uniformly distributed within the grain. Sufficient degassing prior to sintering is critical for forming strong interfaces by facilitating the easy breakup of the oxide film during SPS because Mg powders is highly reactive and form easily Mg oxide on their surfaces, which makes sintering rather difficult. The width of particle boundary in the SPS samples from current experiment appears to be critically depended on degassing vacuum and sintering condition. The removal of continuous or thick oxide stringers with attainment of theoretical sintering density may be a critical parameter for ensuring better mechanical and electrochemical performance in Mg alloys fabricated by high-energy milling SPS process. A fine grained Mg alloy with high toughness and corrosion resistance is obtained by using this degassing process prior to SPS.