Abstract
In this work, the effect of minor Y on the microstructure and corrosion behavior of as-cast Mg-3Zn-1Mn-xY (x = 0,0.5, 1.0, 1.5 and 2.0wt.%) alloys were investigated. The microstructure revealed that the precipitated phases changed obviously in as-cast Mg-3Zn-1Mn-xY alloys accompanying the stepwise addition of Y element. The corrosion results shown that corrosion resistance of as-cast Mg-3Zn-1Mn-xY alloys were primarily strengthened accompanying the addition of Y elements before 1wt.%, while further addition deteriorated this effect. Among them, as-cast Mg-3Zn-1Mn-1Y alloy containing α-Mg + Mg3Zn6Y(I-phase) phase performed lower corrosion rate (CR = 0.571 ± 0.03 mm/y) and largest polarization resistance (Rp = 1129.94 Ω∙cm2) than that of other alloys containing α-Mg + Mg7Zn3 and α-Mg + Mg3Zn3Y2(W-phase) phases, which was mainly ascribed to the strip Mg3Zn6Y phase continuous distributed at grain boundary to hinder corrosion spreading as well lower potential difference |E|= 0.22 V existed between Mg matrix and cathode phases to relax the micro-galvanic effect. In addition, the dominant corrosion films of Mg-3Zn-1Mn-xY alloy were consisted of MgO, Mg(OH)2, hydroxyapatite as well as a small fraction of MgHPO4, they were conducive to the self-repair of the product films to enhance the corrosion resistance of the Mg alloys.