Effects Of Electric Current On Microstructures And Properties Of 7B04 Alloy During Aging Treatments

In this paper,the effect of current intensity on the conductivity,tensile strength,elongation of samples and the number,size,distribution of precipitations after aging with direct current(DC)of different intensities at 110?,120?,130?are studied by conductivity tests,tensile tests,scanning electron microscopy(SEM),X-ray diffraction analysis(XRD),differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).The main results are as follows:(1)The conductivities of the alloy increase first and then decrease with the increase of the current intensity when aged at 110?,120?,130?,and reaching the maximum when aged with DC200A/110?,DC100A/120?,DC100A/130?respectively.When aged at 130? for 12h,the conductivity is 28.5%IACS.The conductivities are 28.9%IACS,28.8%IACS,28.7%IACS respectively aging with DC100A,DC200A,DC400A.(2)When aged at 110? for 24h without current,the tensile strength of the alloy reaches a peak of 671.6MPa;They also reach peak-aging at 24h when aged with DC100A,DC200A,DC400A,the tensile strengths are 689.1MPa,693.8MPa,680.3MPa,respectively,which are higher than that of aging without current,and the tensile strengths of the alloy are the highest when aged with DC200A.(3)The tensile strength is 677.7MPa aging at 120? for 24h without current,and it reachs the peak value,and then prolonges the aging time to 4 8h,the tensile strength decreases by 4.9MPa;When aged with DC60A,DC100A,DC200A and DC400A for 12h,the tensile strengths reach its peak value,which are 695.9MPa,718.2MPa,696.2MPa and 681.6MPa,respectively.Then it tends to be stable with the prolongation of aging time.The peak tensile strengths of the alloy after aging with direct current are higher than that of aging without direct current,and the peak aging time of the alloy are advanced when aged with direct current.(4)The tensile strength reach peak value after aging at 130? for 12h without current,which is 673.3MPa,and then it stabilizes with the prolongation of aging time;The peak tensile strengths are 692.0MPa,684.5MPa and 678.2MPa when aged with DC100A,DC200A and DC400A for 12h,which higher than that of aging without direct current.Then the tensile strengths decrease significantly and softening occurs after prolonging the aging time.(5)Compared with the fracture morphology of aging without current,the dimples are deeper,more abundant and more uniformly distributed after aging with direct current.The elongation of the alloy is 17.4%when aged at 120? for 24h without current.When aged for 24h with DC100A,DC200A,DC400A,the elongations are 19.9%,19.8%and 19.8%,which are higher than that of aging without current.And it corresponds to the fracture morphology.(6)The DSC results indicate that the heat enthalpies of GP zones and ?'phases aging at 110?,120? and 130? with current are higher than aging without current.With the increase of current intensity,the heat enthalpy is bigger,and the peak temperature is higher.The heat enthalpy of this endothermic peak is 7.2J/g when aged at 120?for 24h without current.When aged with DC100A,DC200A and DC400A for 12h,the heat enthalpies are 8.4J/g,9.2J/g,10.3J/g,respectively.(7)The TEM observation shows that there are only a small amount of GP zones and ?' phases precipitated from the matrix after aging at 120? and 130?without current.And the area fractions of precipitations are 15.6%,17,4%,respectively.When aged with DC 100A,the number of the GP zones and ?'phases increase greatly,the sizes are 8.6nm and 7.8nm,which have little change compared with aging without direct current.And the area fractions of precipitations increase to 23,1%and 23.5%,respectively.The sizes of strengthened phases add with the increase of direct current intensity to 200A and 400A,which are 10.5nm,11.3nm and 9.9nm,10.6nm.And the area fractions of precipitations are 25.2%,25.6%and 27.0%,27.1%,respectively.