The Vehicle Sections 6005a And 7005 Alloy Heat Treatment Characteristics

In this paper, the influence of heat treatment on mechanical properties of 6005A and 7005 used as heavy sectional materials for vehicles was studied by transmission electron microscopy (TEM) analysis, tensile tests and hardness measurement. The results show that:The nose temperatures of TTP curves plotted by HB and o bare about 370℃, the quench sensitivity at moderate temperature is quite higher than that of high-temperature zone and the quench sensitivity of low-temperature zone is between them. It is concluded that, in the industrial production of section material, the outlet temperature after on-line extruding should be higher than 480℃, air-cooling time from 480℃ to critical temperature (400℃) should be shorter than 60s~90s and the quench rate should be quick enough at moderate temperature.With the increasing of isothermal time supersaturated solid solution decomposed into equilibrium phase MgiSi continuously. It suppresses the formation of major strengthening phase P ' and is detrimental to mechanical properties of 6005A alloy.The peak hardness of single-stage aged 7005 (105℃50h) is higher than that of alloy after two-stage aging(105℃8h+155℃8h), however, in case of single-stage aging regime the peak hardness is reached during longer exposures.The size, volume fractions and phase composition of hardening precipitates in 7005 are largely depended on the aging regimes. A large volume fraction of fine n ' precipitate particles can be formed in both aging regimes: 105℃8h+155℃8h and 105 ℃50h.But the size of n. ' precipitate particles formed in two-stage aging is larger than that of single-stage aging. At higher aging temperature(1553), equilibrium phase is easy to form in alloy during single-stage aging , thus leading to the poor performance of the alloyAging accleration can be obtained by adopting proper two-stage aging regime (100~120℃s 3~10h+150~170X\ 5~15h) with little loss of strength properties.