固溶条件对7136铝合金挤压型材粗晶环的影响

粗晶环是中高强度铝合金挤压型材常见的组织缺陷之一,揭示铝合金型材的粗晶环形成规律对于制定合理的挤压和热处理制度、进而抑制粗晶环的形成具有重要意义。以7136铝合金挤压型材试样为对象,研究不同固溶条件下试样的粗晶环形成规律,并从再结晶组织和析出相形貌分布特征等方面分析粗晶环的形成原因。结果表明:试样的粗晶环形成最低温度为450℃,且随固溶温度的提高,粗晶环深度逐渐增大;固溶温度470℃保温30 min时粗晶环的深度为63 m。在固溶温度470℃下时,随着保温时间的延长,粗晶环的深度开始增加较快,然后逐渐减慢,60 min后,继续延长保温时间粗晶环深度基本不变。在挤压过程中,试样边部再结晶程度约为心部的两倍,同时,由于边部基体Mg、Zn贫化导致析出相(MgZn2)较少,对晶粒长大的抑制作用较弱,因此,挤压试样在固溶过程中易形成粗晶环。

Effect of solution treatment on peripheral coarse grain structure of 7136 aluminum alloy extruded profile

The peripheral coarse grain(PCG)is one of the common microstructure defects of middle and high strength aluminium alloy extruded profiles.It is important to reveal the formation rule of PCG in aluminium alloy extruded profiles for making reasonable extrusion and heat treatment process and then inhibiting the formation of PCG.The formation of PCG in 7136 aluminum alloy extruded profiles under different solid solution conditions was studied,and the reasons for the formation of PCG was analyzed from the aspects of recrystallization structure and morphology distribution of precipitated phases.The results show that the lowest temperature for the formation of PCG is 450℃,and the depth of PCG increases with increasing solution temperature.The depth of PCG at 470℃for 30 min is 63 m.At 470℃solution temperature,the depth of PCG increases rapidly with the prolongation of holding time,then increases slowly,and continues to prolong the holding time after 60 min,the depth of PCG is basically unchanged.In the extrusion process,the recrystallization degree at the edge of the specimen is about twice as much as that at the core.At the same time,due to the depletion of Mg and Zn at the edge of the specimen,the precipitation of MgZn2 is less and the inhibition of grain growth is weaker,so,the PCG is easy to be formed in the solid solution process of extruded specimen.