Study On Hot Deformation Behavior Of ?B₄Cp+SiCw?/ZK60 Magnesium Matrix Composites

(B₄Cp+SiCw)/ZK60 magnesium matrix composites were prepared successfully by liquid infiltration.Hot compression experimental of the as-cast?B₄Cp+SiCw?/ZK60 composites and ZK60 alloys were preformed at various temperatures and strain rates.The hot compressive behaviors of the composites and the alloys were studied.The effects of processing parameters on hot compressive behaviors of the materials were analyzed,and constitutive equations were established by fitting the peak stress.The processing maps of the composites and the alloys were constructed to obtain optimum hot deformation parameters.Hot extrusion was performed under the optimum parameters conditions.Tensile test of the as-extruded materials was preformed.Microstructure observation of as-extruded materials was employed to investigate the microstructure evolution during extrusion.Heat treatment of solution and aging were preformed,and the influence of the addition of reinforcements on the aging precipitation behavior and properties of the composites were analyzed.Combining precipitation phase appearance,the aging treatment process suitable for?B₄Cp+SiCw?/ZK60magnesium matrix composites was determined.Based on the hot compressive behaviors of as-cast composites and alloys,results showed that the flow stresses declined when the temperature rised or when the strain rate decelerated.The hot compression of the composites and the alloys were controlled by thermal activation,and the flow stresses under the experimental range could be expressed as a function of parameter Z.The activation energy of the composites obtained by the formula of peak stress were greater than the activation energy of the alloys at the same temperature and strain rate,and both of them were greater than self-diffusion activation energy of pure magnesium,which indicated that the dynamic recrystallization were occurred in the composites and the alloys during hot compression.The optimum working regions were identified using the processing maps developed at a strain of 0.3 for?B₄Cp+SiCw?/ZK60composites and ZK60 alloys.The optimum working regions for the composites was the zone of 270-380?and 0.1-1s^-1.Hot extrusion of as-cast?B₄Cp+SiCw?/ZK60 composites and ZK60alloys were performed under the optimum parameters conditions suggested by the processing maps,and extruded rods with great surface quality were got.It manifested correctness and validity of the processing maps of the materials.B₄C particles and SiC whiskers in extruded composite rods distributed along extrusion direction orderly.The reinforcements in composites could provide more heterogeneous nucleation sites for dynamic recrystallization,promote the occurrence of dynamic recrystallization,and restrain the grain growth.Based on the above reasons,the average grain size of the composites was decreased.Compared with as-extruded ZK60 alloys,the elastic modulus,yield strength and ultimate tensile stress of the as-extruded composites were increased by 98.8%,19.7%and 36.4%respectively.According to the age hardening curves,ZK60 alloys underwent three periods including under aged,peak aged and over aged,and appeared aging hardening laws.The aging hardening curves of the composite had no regular change with the increase of aging time,and lacked obvious aging peak.Combined hardness analysis with precipitation phase appearance observation,the heat treatment process of solid solution treatment?400?,8h?and aging process?170?,2h?was an optimum heat treatment process for the composites.