Abstract
The stress corrosion cracking (SCC) properties of the bi-directional forged (BDF) Mg-4Zn-0.6Zr-xSr (ZK40-xSr, x = 0, 0.4, 0.8, 1.2, 1.6 wt %) alloys were studied by the slow strain rate tensile (SSRT) testing in modified simulated body fluid (m-SBF). The average grain size of the BDF alloys were approximately two orders of magnitude smaller than those of the as-cast alloys. However, grain refinement increased the hydrogen embrittlement effect, leading to a higher SCC susceptibility in the BDF ZK40-0/0.4Sr alloys. Apart from the grain refinements effect, the forging process also changed the distribution of second phase from the net-like shape along the grain boundary to a uniformly isolated island shape in the BDF alloys. The SCC susceptibility of the BDF ZK40-1.2/1.6Sr alloys were lower than those of the as-cast alloys. The change of distribution of the second phase suppressed the adverse effect of Sr on the SCC susceptibility in high Sr–containing magnesium alloys. The results indicated the stress corrosion behavior of magnesium alloys was related to the average grain size of matrix and the distribution and shape of the second phase.
Highlights
As biodegradable implant materials, magnesium (Mg) and its alloys have recently attracted increasing research attentions for their ability to completely degrade in the body after fulfilling their temporary function [1,2]
In order to study the effect of microstructure and second phase on the stress corrosion cracking (SCC) susceptibility of the forged ZK40-xSr magnesium alloys, immersion testing, electrochemical analysis, and slow strain rate tensile (SSRT) tests were carried out
The average grain size changed from about 100 μm to below 10 μm after the forging process
Summary
Magnesium (Mg) and its alloys have recently attracted increasing research attentions for their ability to completely degrade in the body after fulfilling their temporary function [1,2]. Mg-based alloys have a close elasticity modulus to cortical bone, which could decrease or avoid the “stress shielding effect”. In comparison with biodegradable polymers, Mg alloys exhibit good mechanical strength. The tensile strength of human bone, PLGA, and Mg alloys are 110–130, 13.9–16.7, and 150–290 MPa, respectively [6]. These make Mg and Mg alloys suitable candidates for orthopedic implants [7] (e.g., bone plate and screw) and cardiovascular [8] (e.g., stent) applications
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