Achieving ultra-high corrosion-resistant Mg-Zn-Sc alloys by forming Sc-assisted protective corrosion product film

The weak corrosion resistance of magnesium and its alloys greatly limited the industrial application.Though functional self-healing coatings have been proposed as countermeasures,repeated damages on coatings under practical installation and complex external environments could require self-adaptive cor-rosion protection against multiple abrasions.In this study,an ultra-high corrosion-resistant Mg-1Zn-1Sc(wt.%)alloy with a corrosion rate of 0.087 mm/y has been designed and prepared,which has fine grains and uniform structure of a nano-scale ScZn phase with low potential.A unique and dense corrosion prod-uct film with a three-layered structure was found and studied on Mg-1Zn-1Sc alloy,providing excellent corrosion protection.In addition,the formation and protection mechanisms of the three-layered corrosion product film on Mg-1Zn-1Sc alloy have been discussed and proposed.The growth behavior of protective corrosion product film could be driven by the synergy of Sc and Zn elements.Furthermore,with the in-crease of Sc content,the strength,plasticity,and corrosion resistance of Mg-1Zn-x Sc(x=0,0.2,0.6,1.0,in wt.%)alloys increased simultaneously.The high corrosion resistance and moderate mechanical perfor-mance qualify Mg-1Zn-1Sc alloy as a promising candidate for diverse industrial applications.

Dependence of corrosion resistance on grain boundary characteristics in a high nitrogen CrMn austenitic stainless steel

Processing schedules for grain boundary engineering involving different types of cold deformation（tension, compression, and rolling） and annealing were designed and carried out for 18Mn18Cr0.6N high nitrogen austenitic stainless steel. The grain boundary characteristic distribution was obtained and characterized by electron backscatter diffraction（EBSD） analysis. The corrosion resistance of the specimens with different grain boundary characteristic distribution was examined by using potentiodynamic polarization test. The corrosion behavior of different types of boundaries after sensitization was also studied.The fraction of low-∑ boundaries decreased with increasing strain, and it was insensitive to the type of cold deformation when the engineering strain was lower than 20%. At the strain of 30%, the largest and smallest fractions of low-∑ boundaries were achieved in cold-tensioned and rolled specimens, respectively. The fraction of low-∑ boundaries increased exponentially with the increase of grain size. The proportion of low-∑ angle grain boundaries increased with decreasing grain size. Increasing the fraction of low-∑ boundaries could improve the pitting corrosion resistance for the steels with the same grain size.After sensitization, the relative corrosion resistances of low-∑ angle grain boundaries, ∑3 boundaries, and ∑9 boundaries were 100%, 95%, and 25%, respectively, while ∑27 boundaries, other low-∑ boundaries and random high-angle grain boundaries had no resistance to corrosion.

Effect of Zn on mechanical and corrosion properties of Mg-Sc-Zn alloys

The effect of different Zn concentrations(0 wt.%,1 wt.%,3 wt.%,and 6 wt.%)on the microstructure,cor-rosion property,and mechanical property of Mg-0.3Sc-x Zn(x=0 wt.%,1 wt.%,3 wt.%,and 6 wt.%)alloys was investigated.Here,MSZ1 alloy exhibits the highest corrosion resistance(0.194 mm/y)and appropriate mechanical properties with an ultimate tensile strength of 228 MPa and elongation of 19%.The superior corrosion resistance of Mg-0.3Sc-1Zn alloys is attributed to the homogeneous volta-potential distribution and the dense corrosion product film.With the increase in zinc content,the strength and plasticity of Mg-0.3Sc-x Zn alloys(x=0 wt.%,1 wt.%,3 wt.%,6 wt.%)improved to some extent.The precipitated ScZn phase plays the role of the second phase strengthening,which enables MSZ6 to obtain the maximum tensile strength.However,the ScZn phase with low volta potential intensifies the galvanic corrosion,re-sulting in the decline of the corrosion performance.