| 6xxx aluminum alloys have experienced widespread use in automotive skin panel applications where relatively high formability and in-service strength are major requirements. Additionally, some parts may require a high level of energy absorption without brittle fracture. In this study, the effects of quench rate and artificial aging on the fracture behavior of alloy 6016 sheet were investigated. Samples of commercially produced 6016 alloy sheet were re-solution heat treated and quenched at various rates prior to aging. Properties and microstructures of samples in T4, T6, and T8 tempers were evaluated. Vickers hardness, tensile, bending, and electric conductivity tests were carried out to show property changes in the sheet as a function of quench rate and artificial aging. Optical, scanning and transmission electron microscopy were used to characterize the microstructure before and after deformation. The experimental results showed that(1) re-solution heat treatment at 565? for 5min is reasonable because the grain size was not obviously different from the as-received commercial sheet(2) rapid quenching retains more solute in solid solution, allowing more clusters to form during natural aging, enabling the alloy to reach higher values of microhardness and yield strength. During a slow quench, coarse precipitates form on grain boundaries and dispersoids, to decreases in strength and bendability.(3) Slow quenching also reduced bendability for sheets aged to the T6 temper. Poor bendability in slowly quenched 6016-T6 sheet was attributed to the occurrence of intergranular fracture. Samples which received a fast quench exhibited higher levels of yield strength and better bendability.(4) pre-strain increased the yield strength in both naturally and artificially aged tempers. Pre-strain creates dislocations which are nucleation sites for ?" phase; so peak aging times for samples in T8 temper were shorter than for T6 temper. |
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