Effect of Microstructure on Corrosion Behavior of WE43 Magnesium Alloy in As Cast and Heat-Treated Conditions

Abstract

The improvement in corrosion resistance of WE43 was well realized by heat treatment. To study the influence of microstructure on the corrosion behavior of WE43 in as-cast and heat-treated conditions, an immersion test was employed with as-cast and heat-treated samples in the 3.5% NaCl solution. The corrosion rate and change of morphology were recorded and the corrosion behavior was further investigated by scanning electron microscopy (SEM). The results indicated that the corrosion rate of the WE43 alloy decreased after heat treatment. It was observed that the eutectic gradually damages the protective film on the surface of the as-cast WE43 in the process of corrosion, which further increases the corrosion rate. The Zr-rich phase formed a domed structure resulting in the adjacent area being further corroded. The Y-rich phase has little effect on the corrosion reaction.

Microstructure, Mechanical, Corrosion, and Ignition Properties of WE43 Alloy Prepared by Different Processes

“…The microstructure consists of α-Mg solid solution and eutectic β phase Mg 14 Nd 2 Y (12 ± 1 wt % of Y, 28 ± 1 wt % of Nd, and 1-2 wt % of Gd and Dy). Additionally, other binary phases such as Mg 24 Y 5 , Mg 3 Nd, and Mg 12 Nd were observed by XRD (Figure 4) which is in accordance with findings in the literature [24][25][26][27]. Although not evident in the XRD spectrum, small cubic-shaped particles in microstructure were analyzed as YH x hydrides according to EDS results.…”

“…In this case, measured lower corrosion rate is associated with a longer time of exposition as the material degrades fast initially, and then it is retarded by the formation of stable corrosion products. Yang et al [27] measured a similar corrosion rate of approximately 1.8 mm•a −1 and 0.5 mm•a −1 in 3.5 wt % solution of NaCl for as-cast WE43 alloy, and aged hot rolled WE43 alloy respectively. Corrosion rates of extruded products in this work are therefore acceptable for bioapplication.…”

“…The heat treatment T4 is performed at 525 • C for 8 h followed by quenching in water in order to dissolve eutectic β phase Mg 14 Nd 2 Y. This material can be subsequently aged at 250 • C for 16 h. During this period new phases precipitate, such as β" (orthorhombic, metastable phase), β (D019, metastable phase), β (Mg 14 Nd 2 Y) [22,23], Mg 24 Y 5 , Mg 3 Nd, Mg 12 Nd, and Mg 41 Nd 5 [24][25][26][27]. The precipitation leads to the improvement of mechanical properties with values of 140-170 MPa for tensile yield strength and 4-7% for elongation in the T6 state [22].…”

“…Corrosion properties strongly depend on the morphology, distribution and shape of the phases. Most intermetallic phases in the WE43 alloy have a corrosion potential close to the Mg matrix, which reduces the effect of galvanic corrosion [27]. Microgalvanic corrosion is a problem of magnesium alloys containing other elements than REEs [28,29].…”

“…Moreover, it was found that the Mg 41 Nd 5 phase has even more negative potential than the surrounding matrix or phases, which improves the overall corrosion resistance [30,31]. The highest difference in potential is between Mg matrix and Zr-rich phases, thus these phases are the most problematic in WE43 alloy from the corrosion point of view [27].…”