In the present research, a composite with a magnesium alloy (WE43) as the matrix and Akermanite as the bioactive and reinforcing agent was fabricated by friction stir processing (FSP), resulting in a microstructure with uniformly distributed fine grains, second-phase particles and micro-sized Akermanite particles. The effect of an addition of Akermanite to the alloy on the mechanical properties and corrosion resistance of the resulting composite was investigated. The compressive strength and ductility of the composite were found to be significantly higher than those of the monolithic WE43 alloy. The value of yield strength of the WE43 sample increased from 75 MPa up to 119 and 225 MPa for WE43-6P and WE43-A-6P samples, respectively. Also, the value of the ultimate compressive strength of the WE43 sample increased from 210 MPa up to 240 and 362 MPa for WE43-6P and WE43-A-6P samples, respectively. The value of elongation for WE43, WE43-6P, and WE43-A-6P samples were 4.5%, 16%, and 22%, respectively. The EIS test showed that the corrosion mechanism of WE43 sample is a combination of localized pitting and uniform corrosion, which shifted towards more uniform corrosion with higher corrosion resistance by applying FSP and adding Akermanite powder. The potentiodynamic polarization and in vitro immersion tests confirmed this finding, as evidenced by the increase in polarization resistance from 0.192 for the monolithic WE43 alloy up to 0.339 and 0.609 kΩ/cm² for WE43-6P and WE43-A-6P samples, respectively. The mass loss rate of the WE43 sample decreased from 20.82 to 10.13 mm per year for the WE43-A-6P sample after 312 h immersion in SBF solution. All tests approved that by applying FSP and adding Akermanite to WE43, the corrosion resistance in the SBF solution could be significantly enhanced.

A composite material based on the WE43 magnesium alloy and containing nano-sized hardystonite ceramic particles was processed by means of friction stir processing (FSP). Compressive strength and strain-at-failure of the WE43 alloy increased as a combined result of FSP and nanoparticle reinforcement. The results of potentiondynamic polarization and electrochemical impedance spectroscopy tests indicated that the corrosion mechanism of the nanocomposite is combination of uniform corrosion and localized pitting corrosion which is not different from the base metal. However, the corrosion rate is significantly decreased as a result of reduced localized corrosion of the base metal after FSP and the effect of hardystonite to reduce pitting corrosion. The polarization resistance is increased from 192.48 to 339.61 and 1318.12 Ω/cm² by applying FSP on WE43 and addition of nano-sized hardystonite particles, respectively. Indeed, the fabricated nanocomposite shows significantly increased corrosion resistance. Enhanced strength, ductility and corrosion resistance were attributed to grain refinement in addition to the fragmentation and redistribution of second-phase particles in the magnesium matrix, occurring during FSP.

Magnesium alloys have many unique properties, mostly benefitting from the low density of magnesium. However, they are not competitive, when compared with other lightweight materials, such as aluminum alloys, particularly in ductility and corrosion resistance. There is a strong need to improve the mechanical properties and corrosion resistance of magnesium alloys. In the present research, friction stir processing (FSP) as a severe plastic deformation process was applied to the WE43 magnesium alloy. The effect of FSP up to 6 passes on the grain structure, second-phase particle distribution, mechanical properties and corrosion resistance of the alloy was investigated. It was found that a continuous network of second-phase particles was present at the grain boundaries, which was considered to be one of the main causes for the poor ductility of the alloy in the as-annealed state. By applying two passes of FSP, the grain structure was significantly refined, changing from an average grain size of 12.4 to 2.5 μm. By further FSP, the grain structure continued to refine to an average grain size of 1.4 μm after 4 passes and remained unchanged after 6 passes. However, the fragmentation and redistribution of second-phase particles continued to occur during the 4th and 6th passes of FSP. Because of these microstructural changes, the uniform strain to maximum stress and the strength of specimens gradually improved with increasing number of FSP passes. The corrosion resistance of the alloy was found to be improved by applying 6 passes of FSP, compared to that of the alloy in the initial as-annealed state, which was attributed to the fragmentation and redistribution of second-phase particles. By applying FSP, the uniformity of the protective passive layer was improved and, in the meantime, the intensity of micro-galvanic coupling leading to pitting corrosion was decreased.