Relationship between Anisotropy of Corrosion Properties of Extruded Alloys AZ31 and ZK60 with Crystallographic Texture and Volume Distribution of Second Phase Particles

Insufficient corrosion resistance of magnesium alloys limits their technical and medical applications. It is known that the corrosion rate of these materials depends, among other things, on the orientation of the samples relative to the workpieces, for example, rods or sheets obtained by thermomechanical processing. There is an opinion in the literature that this is primarily due to the influence of crystallographic texture. In this work, the corrosion resistance of samples cut from extruded rods of industrial alloys ZK60 and AZ31 along and across the extrusion direction was investigated. The corrosion rate was determined by the loss of weight and volume of the samples, as well as by the volume of hydrogen released when they were dissolved in a 0.9% NaCl solution. The microstructure and surface of the samples after corrosion tests were investigated using scanning electron microscopy, energy-dispersive X-ray microanalysis, and electron backscatter diffraction. It is shown that the rod has a pronounced basal texture, and therefore the crystallographic orientation of the grains to the lateral surface of the transverse and longitudinal samples is very different. It was found that samples of both alloys cut across the rod had higher corrosion resistance than longitudinal samples. According to published data, if the anisotropy of corrosion properties were caused by crystallographic texture, then longitudinal samples, on the contrary, should have a lower corrosion rate than transverse ones. Therefore, it is concluded that, in the case of medium- and high-alloy magnesium alloys, the anisotropy of corrosion properties is associated mainly with the nature of the volume distribution of second-phase particles, and not with the crystallographic texture. It is shown that the row arrangement of particles on the surface of longitudinal samples leads to deterioration of corrosion resistance.