Effect of Microstructure Factors on Stress Corrosion Behavior of Mg<i>-x</i>Sn Alloys (<i>x</i> = 2, 5, 8 mass%)

Abstract

The effect of microstructure on the stress corrosion behavior of Mg-Sn alloys was investigated using a bent-beam method. The effects of an Mg 2 Sn phase and Sn in the matrix on stress corrosion were investigated. Mg 2 Sn phase mainly formed at the grain boundary. The volume fraction of the Mg 2 Sn phase increased with increasing Sn content, and the morphology of Mg 2 Sn changed from spherical to a semi-continuous network. The average volume fractions of Mg 2 Sn phase increased from 0.07 ± 0.02% to 5.06 ± 0.92% as the Sn content was increased from 2 to 8 mass%. An increase in the amount of Mg 2 Sn phase increased the pit density, whereas dissolution of the Mg 2 Sn phase into the matrix resulted in decreased pit density. An intergranular cracking mode was observed. The solution heat treatment dissolved the Mg 2 Sn phase and eliminated the micro-galvanic corrosion due to Mg 2 Sn, thereby delaying crack initiation also enhancing stress corrosion resistance. Mg-8%Sn sample through solution heat treatment showed the best stress corrosion resistance.

Stress Corrosion Behavior of Mg–2 mass% Sn Alloy by Equal-Channel Angular Extrusion

“…Miller 32) reported that the alloys, AZ91, AM61, and AS41, interpreted to show a SCC threshold at 40-50% yield strength in distilled water. Thus, from previous studies and our previous work 15,23) , the applied stress was determined to 55 ± 5% yield strength and the elastic modulus of Mg-2Sn alloy was 45 GPa. Samples for the three-point bending tests were ground using silicon carbide abrasive papers to 4000 grit.…”

“…The Sn content in matrix also changed during ECAE process, which reduced about 15-25%. However, in our previous research 15) , we have studied the effect of matrix Sn content on stress corrosion test. We revealed that the effect of matrix Sn from 2 to 8% on SCC was slight and could be ignored.…”

“…For Mg-Sn system, many researches have shown that Sn content has a distinct in uence on the microstructure. In our previous research 15) , we studied on the effect of microstructure factors on stress corrosion behavior with 2, 5, and 8 mass% Sn addition. We found out that Mg-2 mass% Sn alloy showed better stress corrosion resistance.…”