Effect Of Electric Current Pulse On The Solidification Of 7075 Aluminum Alloy

The electric current pulse (ECP) remarkably influences on solidification processes of metal. In recent years, studying effect and mechanism of ECP on solidification structure is an important item in field of material preparation. The effect of ECP on solidification structure of 7075 aluminum alloy is experimentally investigated and the refinement mechanism of ECP on solidification structure of 7075 aluminum alloy is analysed.Paper studied the influence of the peak pulse current, pulse frequency and duty cycle to the solidification organization of 7075 aluminum alloy, show that:with an increase of the peak value and frequency of current or decrease of pulse width, macro-alloy solidification structure gradually transformed from coarse columnar crystals into fine equiaxed and equiaxed grain zone area also increased; The average of grain size decreased by 0.82mm to 0.24mm, and the refining effect was obvious. The α-Al primary phase of micro structure transformed from the untreated strip of coarse dendrites into small rose-shaped equiaxed, and with increasing pulse current, the amount of primary phase α-Al gradually increased, the average length of a dendrite was gradually reduced by 0.511mm to 0.121mm; the average of secondary dendrite arm spacing decreased from 0.052mm, until it disappeared.From the study of SEM topography of precipitation phase and component graph in the cast microstructure of 7075 aluminum alloy, we can found that, with an increase of the peak value and frequency of current or decrease of pulse width, the counts of α-Al primary phase in the grain boundaries gradually increased, the counts of α-Al increased gradually from 179 to 220, close to the counts of the internal grain boundary and composition distribution became uniform; the counts of Mg was reduced from 30 to 25, the elements better melted into the grain, and micro-segregation had been greatly improved.Through the analysis of the grain shape, grain size and composition uniformity of pulse current, we determined the best process parameters of effect of EPC on the solidification of 7075 aluminum alloy:peak current 300A, pulse frequency of 150Hz,10% duty.The effect of ECP on solidification nucleation and growth process was studied by theories of electrodynamics and electromagnetic, and the mechanism of the effect of ECP on solidification nucleation and growth process was theoretically studied.