Based on analysis of the main forming methods for double-layer tube,a new short-term forming process called thixo-co-extrusion was put forward in producing double-layer tube by combining the semi-solid forming technology and multi-billet extrusion technology.By means of forward extrusion with shaft,a finite element model of thixo-co-extrusion with A356/AZ91 was constructed by ABAQUS FEM software.The distributions of temperature field and velocity field as well as the contact force during thixo-co-extrusion were studied.The diffusion on the interfaces between inner and outer metals was analyzed.The simulation results show that,in the beginning of thixo-co-extrusion,the uneven wall thickness can appear.To thickness ratio of 5:5,a double layer tube with good inner and outer wall combination can be realized if VA356 is 0.12 m/s and VAZ91 is 0.20 m/s.
The rapid development of electronic packaging industry has resulted in higher requirement for packaging materials.The packaging material of SiC reinforced A356 aluminum alloy was fabricated by mechanical mixing method,and the SiCp/Al composite billet was formed by thixo-forging to manufacture the electronic packaging shell.The microstructure of the produced part was investigated.Two different thixo-forging procedures for manufacturing electronic packaging shell were analyzed.The results show that after being heated to 600 ℃ and held for 3 h,SiCp has good compatibility with A356 aluminum alloy and the SiCp/A356 composite billet can meet the requirements of thixo-forging.When the billet was remelted to 580℃,held for 10 min,the homogeneous microstructure with the best thixo-formability can be realized.The thixo-forging of electronic packaging shell is feasible.
