Microstructure And Mechanical Properties Of Al₃Ti Or Al₃Ti+AlN Reinforced Al-Mg-Mn Composites Prepared By Vibration And Pressure Fiel

Aluminum matrix composites are widely used in military,aerospace,automotive and shipbuilding industries due to their excellent mechanical and physical properties such as low density,high specific strength,high specific stiffness,favorable dimensional stability,good electrical and thermal conductivity.The problem of wettability between reinforcing phases and matrix can be effectively solve by in situ synthesis,which is one of the main research directions of aluminum matrix composites.In this context,using Al₃Ti and Al N as reinforcing phases and Al-Mg-Mn alloys as matrix,with ultrasonic and mechanical vibration coupling field and squeeze casting process being combined,the effects of ultrasonic mechanical coupling field,squeeze casting process,Ti and Si₃N₄ content on the microstructure and mechanical properties of Al-Mg-Mn alloy were studied by means of optical microscope（OM）,X-ray diffraction（XRD）,scanning electron microscope（SEM）and tensile property test.The following conclusions are obtained:（1）The coupling effect of ultrasonic and mechanical vibration can promote the in-situ reaction and disperse and refine Al₃Ti particles.Under the effect of the coupling at 760°C for 10 minutes,the tensile strength,yield strength and elongation at room temperature of Al₃Ti/Al-Mg-Mn matrix composites were 222 MPa,119 MPa and 8.1%,respectively.Compared with Al-Mg-Mn matrix,the tensile strength and yield strength at room temperature of Al₃Ti/Al-Mg-Mn matrix composites were increased by 17.5%and 25.2%respectively,and the elongation was decreased by 0.6%.The improvement of mechanical properties at room temperature was mainly attributed to grain refinement strengthening,load transfer strengthening and thermal mismatch strengthening caused by Al₃Ti reinforcing phase,among which the thermal mismatch strengthening contributed the most to the improvement of the strength of composites.（2）Applying pressure during the solidification of the melt can effectively reduce the casting defects of the alloy.The more Ti content in the composite,the more Al₃Ti particles were generated,and the porosity of the composite increased with the increase of Al₃Ti content in the alloy at the same pressure.When the Ti content was 3%,the generated Al3Ti content in the composite reached 12.3%.Compared with the matrix,the tensile strength and yield strength of the composite increased by 28%and 47.3%,respectively,while the grain refinement increased by 66%,but the elongation decreased by 12%.（3）compared with Al-Mg-Mn alloy,the grains of Al₃Ti+Al N/Al-Mg-Mn composites were refined and the mechanical properties were improved.The elongation of Al₃Ti+Al N/Al-Mg-Mn composites was higher than and the tensile strength was lower than that of Al₃Ti/Al-Mg-Mn composites with the same Ti content.This was mainly due to the incomplete coating of Si₃N₄ powder by Ti powder,which hindered the reaction between Ti powder and aluminum melt,resulting in the decrease of Al₃Ti content,which improved the elongation of the composites and reduced the tensile strength of the composites.