Comprehensive experiment on preparation and characterization of CrCoNi/AZ31 magnesium-based composite materials
[Objective]To promote the widespread adoption of magnesium-based composite materials in lightweight structural applications,it is essential to develop and apply appropriate plastic forming processes to enhance their processing performance.Particle reinforcement and grain refinement are effective approaches to strengthening magnesium alloys.Metal particle reinforcement exhibits excellent mechanical properties and significantly strengthens magnesium alloys.[Methods]In this experiment,different mass fractions of CrCoNi particles were mechanically ball-milled with AZ31 magnesium alloy.The milled powders were subsequently sintered using spark plasma sintering technology to obtain composite specimens with CrCoNi mass fractions of 2.5wt％,5wt％,and 10wt％.The sintered specimens were processed and characterized using X-ray diffraction(XRD)analysis and scanning electron microscopy(SEM)to investigate the microstructure and degree of grain refinement of the powder metallurgy-prepared CrCoNi/AZ31 magnesium-based composite materials.Mechanical performance testing was conducted on the CoCrNi/AZ31 composite to study the effect of CrCoNi particles on the hardness of the composite material.Subsequently,the samples underwent isothermal compression tests at temperatures of 250 ℃,300 ℃,350 ℃,and 400 ℃,and strain rates of 0.001 s,0.01 s,0.1 s,and 1 s-1 to analyze the influence of temperature and strain rate on CrCoNi/AZ31.[Results]The addition of CrCoNi particles leads to grain size refinement in the composite material,with the alloy's grain size decreasing as the content of CrCoNi particles increases.Owing to the high hardness of CrCoNi particles themselves and the grain refinement effect,the hardness of the composite material is significantly enhanced.Calculations using the Williamson-Hall method revealed that the variation in XRD diffraction peak width of the composite material with added CrCoNi particles is independent of lattice microstrain but solely dependent on material grain size.SEM analysis indicated the formation of the Al13Cr2 phase in the post-sintering CrCoNi/AZ31 magnesium-based composite material,exhibiting good interface bonding.Both the strengthening and intermediate phases contribute to grain refinement.In the compression experiments,at a constant compression deformation temperature,increasing the compression strain rate led to an increase in the material's peak stress(up)and overall flow stress.[Conclusions]We investigated how different contents of CrCoNi particle reinforcement affect the matrix microstructure and analyzed its phase composition.Under the same compression deformation strain rate,increasing the deformation temperature resulted in a decrease in the material's peak stress(ap)and overall flow stress.The CrCoNi particle strengthening phase significantly refines the matrix,with phase composition including CrCoNi,Al13Cr2,and Mg,exhibiting good interface bonding between the matrix and the strengthening phase.The addition of CrCoNi particles results in a notable increase in material hardness.Specifically,the 5wt％CrCoNi/AZ31 composite material has an average grain size and hardness of 5.02 μm and 17 6HV,respectively.
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