【作者】 宋华华；

【导师】 蒋大鸣；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2010， 硕士

【摘要】 本文通过光学显微镜、扫描电镜、差热分析、透射电镜、X射线衍射分析、硬度、拉伸试验、电导率测试等分析测试方法,系统研究了均匀化、固溶、时效工艺对Al-Zn-Mg-Cu系合金B96显微组织和力学性能的影响,得出了B96铝合金最佳的热处理工艺,为B96铝合金的工业化生产提供了实验依据。合金的铸态组织分析表明:半连续铸造生产的铝合金中存在严重的枝晶偏析,合金中的非平衡相呈网状分布在晶界上,这些非平衡相主要是MgZn₂（η）相和Al₂Mg₃Zn₃（T）相,其中MgZn₂（η）相呈片层状分布,Al₂Mg₃Zn₃（T）相呈块状分布。在单级均匀化情况下,随着均匀化温度的升高和时间的延长,铸态合金中的网状组织逐渐消失,粗大的第二相逐渐减少;经过470℃/24h均匀化后,合金中的MgZn₂（η）相基本消除,但仍有块状的Al₂Mg₃Zn₃（T）相剩余。当合金均匀化温度超过480℃时,合金发生轻微的过烧现象。双级均匀化采用470℃保温24h后升温到480℃均匀化不同的时间,随着第二级均匀化时间的延长,合金中剩余的第二相继续溶解,时间超过12h后合金中的晶粒发生长大现象,影响合金时效后的性能。合金的最佳双级均匀化工艺为470℃/24h+480℃/12h,此时的合金经过固溶时效后的抗拉强度和屈服强度比单级均匀化提高20MPa左右,延伸率提高6%左右。固溶和时效处理研究表明:随着固溶温度的升高,合金中剩余的第二相逐渐减少,过饱和度增加,时效后合金的抗拉强度、屈服强度和延伸率都有所提高,但温度过高会发生过烧和晶粒长大现象,影响合金时效后的性能;时效温度和时效时间均会影响合金的组织及力学性能。在欠时效状态,合金的析出相细小弥散,体积分数较小,晶界上的析出相呈连续分布;在峰值时效状态,合金中第二相仍呈细小弥散分布,体积分数增加;在过时效状态,合金中的晶内析出相呈短棒状或者长条状分布,析出相的密度下降,析出相间的距离增大,晶界上的析出相呈断续的条状分布。更多还原

【Abstract】 The influence of homogenization, solution and aging treatment on the microstructure and mechanical properties of an Al-Zn-Mg-Cu alloy was investigated systematically using optical microscope,scanning electron microscope, differential scanning calorimetry, transmission electron microscope, X-ray diffraction analysis,hardness, tensile test,conductivity tests etc. The optimum processing of the heat treatment was obtained, which provided an experimental basis for the industrial production.The research showed that the as-cast microstructure of the alloy exhibited apparently dendrite segregation phenomena,non equilibrium eutectic structure was on the grain boundary, with the occurrence of network. Most of these non equilibrium phase was MgZn₂（η）and Al₂Mg₃Zn₃（T）phase, MgZn₂（η）phase was schistose, and Al₂Mg₃Zn₃（T） was massive phase.During the course of one-step homogenization treatment, the dendrite structure and coarse equilibrium phase disappeared gradually as the homogenization temperature increased and the homogenization time prolonged. MgZn₂（η） phase was almost disappeared by the homogenization treatment of 470℃/24h, but the massive phase Al₂Mg₃Zn₃（T） still keep remanent, the alloy was overburnt slightly when the homogenization temperature was over 480℃.Two-step homogenization treatment was 470℃/24h+480℃for different holding time. The remanent second phase dissolve gradually, the grains growed up when the second stage homogenization time exceed 12h, which can effect properties of the alloy. The optimum processing of the two-step homogenization treatment was 470℃/24h+480℃/12h. The tensile strength and yield strength was increased about 20 Mpa, and the elongation was increased 6%.Studies on the solution treatment and aging showed that the remanent second phase decreased and the supersaturation increased as the homogenization temperature increase, the tensile strength, yield strength and elongation after aging was increased, but the over-high temperature resulted in overburnt and the grains grew up, which would affect the property of the alloy.Both aging temperature and aging time affeted the microstructure and mechanical property of the alloy, at under-aged state, ageing precipitates were finer and more dispersive, the volume fraction was lower and precipitates on the grain boundary were continuous. The microstructure of the peak-aged alloy still consists of fine dispersed precipitates and precipitates on the grain boundary are continuous, and the volume fraction was increased. At over-aged state, precipitates was rod-like, and the density decreased, the distance between precipitated phases became larger, precipitates phases was rod-like,which intermittent scattered on the grain boundary.更多还原