Evading strength-corrosion tradeoff in Mg alloys via dense ultrafine twins

Abstract

Conventional ultrafine-grains can generate high strength in Mg alloys, but significant tradeoff of corrosion resistance due to inclusion of a large number of non-equilibrium grain boundaries. Herein, an ultrafine-grain structure consisting of dense ultrafine twins is prepared, yielding a high strength up to 469 MPa and decreasing the corrosion rate by one order of magnitude. Generally, the formation of dense ultrafine twins in Mg alloys is rather difficult, but a carefully designed multi-directional compression treatment effectively stimulates twinning nucleation within twins and refines grain size down to 300 nm after 12-passes compressions. Grain-refinement by low-energy twins not only circumvents the detrimental effects of non-equilibrium grain boundaries on corrosion resistance, but also alters both the morphology and distribution of precipitates. Consequently, micro-galvanic corrosion tendency decreases, and severe localized corrosion is suppressed completely. This technique has a high commercial viability as it can be readily implemented in industrial production.

Effects of Severe Plastic Deformation and Ultrasonic Treatment on the Structure, Strength, and Corrosion Resistance of Mg-Al-Zn Alloy

“…On the other hand, twins of system can increase the corrosion resistance. This is related to the high oxidation activity of atoms in the twin plane as compared with atoms in the densely packed basis plane [ 52 , 53 ], which allows for the easier formation of the oxide film or reduced effects of corrosion anisotropy in misoriented areas in the materials. Twin boundaries are fully coherent and have a lower inter-phase energy than some non-coherent grain boundaries.…”

Comprehensive review of additively manufactured biodegradable magnesium implants for repairing bone defects from biomechanical and biodegradable perspectives

“…Hydrogen precipitation is the primary cathodic reaction for Mg because its electrode potential is considerably lower than the equilibrium electrode potential for the H reaction. The Mg matrix typically suffers from severe anode dissolution owing to non-equilibrium grain boundaries caused by the poor corrosion resistance of Mg alloys (Yan et al, 2021). Therefore, the overall Mg corrosion reaction produces Mg(OH) 2 and H 2 (Eq.…”

Towards development of a high-strength stainless Mg alloy with Al-assisted growth of passive film

“…For example, the corrosion rate of Mg-RE binary alloys increases exponentially with increasing RE content 20 , which is attributed to the formation of galvanic cells between RE-containing secondary phases and the magnesium matrix 20 – 22 . Although some researchers have proposed strategies to simultaneously improve the strength and corrosion resistance with alleviating the side-effect of secondary phases 23 – 25 , and a promising strength-corrosion synergy was recently achieved via dense ultrafine twins 26 , the issues remain that either the overall properties are far from satisfaction 23 , 24 or the fabrication process is complicated 26 . It is worth mentioning that the corrosion rate of Mg-RE binary alloys could be reduced by the addition of a third alloying element accompanied with microstructure optimization.…”