Stress corrosion cracking behavior of an as-extruded Mg-1.8Zn-0.5Zr-1.5Gd magnesium alloy in a simulated body fluid

Abstract

The microstructure, corrosion resistance, and stress corrosion cracking behavior of an ascast and solid-solution Mg-1.8Zn-0.5Zr-1.5Gd biomagnesium alloy after extrusion deformation were studied. Results show that when the extrusion ratio was 7.7 and the extrusion temperatures were 350 and 360 • C, the as-cast and solid-solution alloys underwent complete dynamic recrystallization, and the grains were significantly refined. The precipitated phase in the extruded alloy is mainly composed of a nano-scale (Mg, Zn)3Gd and an Mg2Zn11 phase. A small amount of undissolved and broken micron-sized (Mg, Zn)3Gd phase particles appeared in the as-cast extruded alloy. The electrochemical corrosion produced during the stress corrosion process peeled off the (Mg, Zn)3Gd phase particles and induced rapid dissolution of the adjacent matrix. As a result, stresses were accumulated, and stress corrosion sensitivity occurred. At the same time, some larger-sized cracks appeared in the tensile fracture of the alloy. The difference in grain size and orientation in different regions of the solid-solution extruded alloy leads corrosion fracture to be composed of parallel grooves in different directions. Solution treatment of the magnesium alloy was found to reduce the stress corrosion susceptibility of extruded magnesium alloy and make it promising as a biodegradable implanting material.

Influence of Severe Plastic Deformation by Extrusion on Microstructure, Deformation and Thermal Behavior under Tension of Magnesium Alloy Mg-2.9Y-1.3Nd

“…The structure for the extruded state is dominated by a weak crystallographic texture of the <001> type. The inverse pole figures are presented for different external sections in the crystal: longitudinal X0, transverse Y0, and normal (axial) Z0 in three main planes (0001), (01-10), (11)(12)(13)(14)(15)(16)(17)(18)(19)(20). As one can see, in the recrystallized state, the inverse pole figures have clear maxima (Figure 4a), and the maximum reflection density is not concentrated near a particular crystallographic direction.…”

“…The latter are due to magnesium's ability to release hydrogen during biodegradation, which has a cytopathogenic effect on tumor cells [11,12]. Finally, magnesium alloys have an optimal modulus of elasticity (40)(41)(42)(43)(44)(45), similar to that of the native bone [13,14]. Alloying of magnesium with rare earth metals (RE), such as Y, Nd, Gd, Ce, Dy, etc., leads to the enhancement of strength characteristics, and to increases in plasticity and corrosion resistance [15][16][17][18].…”

“…In view of the above, various deformation methods were proved to be very promising, including severe plastic deformation (SPD), for example, equal-channel angular pressing (ECAP), abc-forging, rotational forging, extrusion, etc. These methods allow one to obtain a high level of mechanical properties in metals by grinding grain to an ultrafine-grained (UFG) state [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. In this case, it becomes possible to significantly improve the mechanical properties of alloys.…”

Corrosion and Protection of Magnesium Alloys: Recent Advances and Future Perspectives

“…The rapid dissolution of the matrix near the second-phase particles and the shedding of the second-phase particles will lead to large corrosion cracks in the corrosion fracture. The difference in grain size and orientation determines the different propagation directions of cracks during stress corrosion cracking [37].…”