Preparation Of Semi-solid Slurry By The Serpentine Channel And Rheo-diecasting Procsess Of A380Aluminum Alloy

The A380aluminum alloy is investigated in this paper, the influence of serpentine channel pouring process parameters and Si content on microstructure of the semi-solid A380aluminum alloy slurry is systematically studied, and the flowing pattern of A380alloy melt in the serpentine channel, the distribution of the boundary layer and the formation and evolution of the primary---A1during solidification are discussed moderately. On the basis of above mention, semi-solid A380aluminum alloy slurry is rheo-diecasted by preparation system and rheo-diecasting system apart. The influence of process parameters on die casting filling performance and the mechanical properties of the tensile samples is further studied. Moreover, a reasonable heat treatment process is instituted. The result show as follows:(1) Reducing the pouring temperature, increasing the number of turns or reducing the channel diameter all can improve the quality of the semi-solid slurry, but the mass of solidified shell will increase. The optimum matching parameters of preparation A380aluminum alloy slurry for the graphite serpentine channel are as follows:D20-S5serpentine channel with630-650℃. The average diameter and shape factor of the primary a-Al grains are48μm and0.84, respectively. The optimum matching parameters of preparation A380aluminum alloy slurry for the water-cooling-copper serpentine channel are as follows: serpentine channel is D30-T4, flow of cooling water is500L/h and pouring temperature is630-650. The average diameter and shape factor of the primary α-A1grains are47μm and0.86, respectively. When Si content in A380aluminum alloy is too high, it is unfavorable to use serpentine channel to prepare the semi-solid slurry, satisfied semi-solid A380aluminum alloy slurry can be prepared by water-cooling-copper serpentine channel with low pouring temperature or high cooling-water flow.(2) The flow pattern of the A380aluminum alloy melt in the serpentine channel is simulate by transparent serpentine channel, which is alternately in laminar and turbulent flow pattern. The initial solidification of A380aluminum alloy melt occurs on the serpentine channel wall through Chilling nucleation and heterogeneous nucleation. Part of the free crystal grows to spherical crystal directly, and the other grows to dendrites. Under the turbulent "self-stirring" of alloy melt the dendrites neck down, fuse and evolve to the rosette or nearly spherlization grains. The residual liquid of the semi-solid slurry occur secondary solidification and forms the non-dendrites in the collective crucible.(3) Statistical analysis of the length of the mold-filling samples shows that mold-filling capacity of semi-solid slurry can be strengthened with the increase of the pouring temperature, injection pressure or the mould temperature. When pouring temperature is650℃, mold temperature is200-250℃, holding time is0s and injection pressure is105MPa the mold-filling capacity is the strongest, and the spiral mold is fully filled. It declines with increasing holding time. The semi-solid slurry after holding60s has the weakest mold-filling capacity.(4) The injection pressure, the holding time and the Si content in A380aluminum alloy have very obvious influence on the microstructure of the tensile samples, but the pouring temperature and mold temperature have little influence. The mechanical properties of tensile samples increase with the pouring temperature lowering, injection pressure enlarging or mold temperature increasing, of which the injection pressure are of the most significance. When the pouring temperature is650℃, mold temperature is200-250℃, holding time is0s and the injection pressure is105MPa, the tensile strength is312MPa, the corresponding extension rate was5.6%, and the microhardness is111HV. When the semi-solid slurry after holding the mechanical properties of tensile samples fust increased and then decreased(5) The optimum T6heat treatment of the tensile samples is solution treatment for2h under490℃and the aging treatment for48h under165℃. After the tensile samples are treated by T6heat treatment the maximum tensile strength of the tensile samples is326MPa, the corresponding extension rate is7.03%, and the micro hardness is131HV. The fracture mode will transfer from the cleavage fracture to ductile fracture with the extension of aging treatment time. The precipitates in brittle fracture are Fe and Mn rich phase, which severely decrease the mechanical properties of the tensile sample.