Effects Of Electric Current On Microstructures And Properties Of 6061 Alloy During Aging Treatments

The 6061 alloy extruded profiles were taken as the research material in this paper.Applying different intensities of direct current during the aging process,the conductivity tests,tensile tests,scanning electron microscopy（SEM）,X-ray diffraction analysis（XRD）,differential scanning calorimetry（DSC）thermal analysis and transmission electron microscopy（TEM）were used to investigate the influence of current intensity on the conductivity,tensile properties and aging hardening precipitates.The main results are as follows:（1）When aging at 150℃,170℃ and 180℃,the conductivity of the alloy increased with the increase of the current intensity during the aging process.When aging at 170℃ for 12h without current,the conductivity of the alloy is 42.6%IACS.When aging for 12h with direct current of 100A and 300A,the conductivity are 42.8%IACS and 43.6%IACS,respectively.（2）The tensile strength of the alloy is 291.3MPa and does not reach the peak strength when aging at 150℃ for 48h without current.When aging for 48h with direct current of 100A,the tensile strength is 298.6MPa.The tensile strength increases to 336.3MPa after aging for 48h,and still shows an increasing trend.（3）The tensile strength of the alloy is 315.5MPa and does not reach the peak strength when aged at 170℃ for 24h without current.When aging for 6h with direct current of 100A,the tensile strength reaches the peak value of 372.1 MPa.The tensile strength of the alloy is 352.7MPa after aging for 6h with direct current of 300A,and after that the tensile strength decreases rapidly,the anti-aging softening ability of the alloy is also poor.（4）The tensile strength of the alloy is 334.8MPa and reaches the peak strength when aging at 180℃ for 8h without current.When aging for 6h with direct current of 100A,the tensile strength is 319.1 MPa.The tensile strength of the alloy reaches the maximum value of 324.5MPa after aging for 4h with direct current of 300A.The peak aging time shortening with the increase of current intensity,but the peak strength of the alloy reduces.It can be seen that a certain intensity of direct current can reduce the peak aging temperature,shorten the time to peak aging,and increase the peak strength.（5）The TEM observations show that there are a small amount of β" phases about 27nm in the alloy after aging at 170℃ for 24h without current.There are a large number of β" phases with the size of 8nm distributed dispersedly in the matrix,when it aging for 6h with direct current of 100A.After aging for 6h with direct current of 300A,the average size of β" phase is 15nm.Compared with samples aging for 6h with direct current of 100A,the length of β" phase increases and precipitation density decreased.The main phase in the alloy is β’ which is over-aged structures and β"phase disappeares basically when aging for 24h with direct current of 100A and 300A.（6）The average size of β" phase in alloy at 180℃ for 8h without current is 10nm,and are 15nm and 30nm respectively in alloy aging for 6h with direct current of 100A and aging for 4h with direct current of 300A.It can be seen that the electric current increases the size of β" phases and dreases the quantity of β" phases in alloy aged at 180℃.