Corrosion and stress corrosion cracking of ultra-high-purity Mg5Zn

Abstract

This paper reports on the measurement of the corrosion rate, and the stress corrosion cracking threshold stress, for ultra-high-purity Mg-5Zn. The corrosion rate was higher than the intrinsic corrosion rate of ultra-high-purity Mg, attributed to the quality of the corrosion product film. The threshold stress for stress corrosion cracking, at an applied stress rate of 0.00016 MPa s -1 , was equal to 0.7 times the yield stress in air. The ductility of the cracking indicated that the stress corrosion cracking mechanism was probably hydrogen enhanced localized plasticity.

Stress corrosion cracking of several hot-rolled binary Mg–X alloys

“…The SCC of the hot-rolled Mg-X alloys (Mg0.1Zr, Mg0.1Sr, Mg1Mn, Mg0.3Si, Mg5Sn, Mg0.7La, Mg0.9Ce, Mg0.6Nd, Mg6Al, Mg5Gd and Mg0.3Ca) was studied using linearly increasing stress tests (LISTs) [49] in laboratory air and in distilled water (DW), as in our prior studies of the SCC of Mg alloys [20,22]. The specimen was at one end of a lever arm, while on the other side there was a moveable known mass, driven away from the equilibrium position by a synchronous motor at a linear rate.…”

“…The threshold stress and the ultimate tensile stress have been reported as the applied engineering stress, using the original specimen cross-section area, as in our prior work [22,51]. The ultimate tensile stress, σ UTS , was determined from the position of the movable weight at the end of each test, when the specimen fractured.…”

“…Distilled water by itself is sufficient. Similarly, Bobby Kannan et al [21] found that ZE41, QE22 and EV31A were susceptible to SCC in distilled water, and Shi et al [22] found that ultra-high-purity Mg5Zn suffered SCC in distilled water. It is well established [15, 17-20, 23, 24] that hydrogen plays an important role in the mechanism of the SCC of Mg alloys.…”

Stress corrosion cracking of high-strength AZ31 processed by high-ratio differential speed rolling

“…Stress corrosion cracking was studied using the Linearly Increasing Stress Test (LIST) [37] as in our prior studies of the stress corrosion cracking of Mg alloys [24][25][26][28][29][30]. The specimen was a sheet tensile specimen with gauge length of 20 mm, gauge width of 2 mm, thickness equal to the sheet thickness, and long specimen direction in the plate rolling direction (i.e.…”

“…TGSCC involves hydrogen [1,27]. Our subsequent studies of Mg SCC include studies of Mg-X alloys [28,29], and ultrahigh-purity Mg5Zn [30].…”