Stress Corrosion Cracking of Rare- Earth Containing Magnesium Alloy EV31A Compared With AZ91E Using Slow Strain Rate Test

Padekar, Bharat S. (IITB-Monash Research Academy) | Singh Raman, R.K. (Department of Mechanical & Aerospace Engineering & Department of Chemical Engineering Monash University) | Raja, V.S. (Department of Metallurgical Engineering and Materials Science Indian Institute of Technology Bombay) | Paul, Lyon (Magnesium Elektron Ltd)

OnePetro 

ABSTRACT:

Stress corrosion cracking (SCC) of the high performance rare-earth (RE) containing magnesium alloy Elektron 21 (ASTM - EV31A) was studied using slow strain rate test. Glycerol, distilled water, and 0.01 N and 0.1 N NaCl solutions saturated with Mg(OH)2 were employed. For comparison a wellknown AZ91E alloy was also studied. SSRT studies indicate that both the alloys were susceptible to SCC to some extent in 0.1 N, 0.01 N NaCl solutions and distilled water. However, EV31A showed higher SCC resistance than AZ91E. The fractography of SSRT tested AZ91E and EV31A specimens were largely found to be transgranular in distilled water. However in 0.1 N and 0.01 N NaCl solutions AZ91E exhibited transgranular, while EV31A showed mixed TGSCC and intergranular (IGSCC) fracture involving hydrogen embrittlement. EV31A showed lower susceptibility to SCC in all the three solutions than AZ91E, that is there is not much loss in mechanical properties of EV31A as compared to that of AZ91E in these environments.



INTRODUCTION

Magnesium alloys are materials of choice for structural applications primarily because of their light weight, being only 2/3 density of aluminium. A range of alloys from magnesium –aluminium alloy AZ91, to the highest strength high temperature magnesium – zirconium alloy WE43 are commercially available. Rare-earth addition to magnesium alloys has a significant effect on the creep resistance, which is primarily attributed to the formation of rare-earth containing phases along the grain boundary of the alloy.1, 2 Controlled addition of the individual rare-earth elements in magnesium alloys influence the castability and age-hardening response.3 Magnesium alloys containing aluminium are known for their high susceptibility to general and localized corrosion such as pitting and stress corrosion cracking (SCC). Song et al. 4 mention that the role of anodic dissolution is to produce surface defects which promote hydrogen production and entry in to the material.