To gain a better understanding of thixoforging for the Al_(2)O_(3)-37%Al composite,its mechanical behavior in the pseudo-semi-solid state was studied by isothermal compression tests.The results show that the values of peak stress obviously decrease with increasing temperature and decreasing strain rate.The compressive true stress-strain curves of the Al_(2)O_(3)-37%Al composite can be divided into four stages.They are rapidly ascending,decreasing,steady and slowly ascending.Moreover,the main deformation mechanism controlling deformation of the composite in the pseudo-semi-solid state is the sliding or rotary movement between solid particles.
A new technology thixo-die-forging of the composite in pseudo-semi-solid state was proposed based on the powder metallurgy technology combing with semi-solid metal process,and the cup shells with Al/Al2O3 composite was prepared successfully.The metallographic analysis and performance test show that the microstructure of parts is dense and mechanical properties are excellent with the volume fraction of Al is 37%.The bend strength and fracture toughness of the composite are about 570-690 MPa and 8.5-16.8 MPa·m1/2,respectively.Comparing with reaction in situ and high temperature oxidation technologies the bending strength and fracture toughness are improved greatly.At the same time,it shows that the technology parameters have great influences on the properties.So it is feasible to prepare metal/ceramics composites by the proposed technology.
The temperature field of AZ91D magnesium alloy extruded by equal channel angular extrusion(ECAE) has been simulated using finite element method(FEM).A series of tests were designed to obtain the simulation parameters:flow stress of AZ91D,friction factor and heat transfer coefficient.The simulated temperature agrees well with the measured one.The evolution of temperature and influencing factor was discussed in details.Furthermore,the extrusion pressure of ECAE was analyzed.
