等通道转角挤压与后续冷镦成形过程中7050铝合金紧固件的微观组织演变规律

Microstructure evolution of 7050 Al alloy fasteners during cold upsetting after equal channel angular pressing

等通道转角挤压(ECAP)与冷镦(CU)新型复合成形工艺对获得超细晶高强紧固件具有重要意义。但是目前其复合成形过程中的微观组织演变规律及其与力学性能的关系尚不明确。本文通过透射电子显微技术、电子背散射衍射以及力学性能测试等方法,发现随着位错的不断积累,材料的强度与复合成形工序呈正相关。同时,在大量位错的作用下,变形后的晶粒尤其是在ECAP-CU复合成形后的晶粒内部产生了超细晶粒。经过复合成形后的超细晶紧固件头部存在较多的高密度位错墙、位错胞以及剪切带,并且在剪切带中形成了层状结构。在复合成形过程中剪切力和塑性应变累积的共同作用下,这些细晶和层状结构发生重新排列,使材料内部产生强的(011)<211>(黄铜)织构。该研究为高强铝合金紧固件的成形制造提供了理论参考,有助于复合成形加工工艺的选择和改进。

The innovative combination of equal channel angular pressing(ECAP)and cold upsetting(CU)is significant for producing high-strength Al alloy fasteners with ultrafine grains.However,the relationship between microstructure evolution and mechanical strength during composite deformation remains unclear.In this study,using transmission electron microscopy,electron backscatter diffraction,and mechanical property tests,it is found that the mechanical strength increases with each step of composite forming operations due to the accumulation of dislocations.Forest dislocations also contribute to the generation of ultrafine grains within deformed grains,particularly in ECAP-CU processed grains.Moreover,we observe the formation of lamellar structures within the shear bands in the head of the ultrafine grain fastener after final composite deformation,which is full of dense dislocation walls and dislocation cells.The rearrangement of these fine grains and lamellar structures yield a strong(011)<211>(brass)texture during composite deformation under the effect of shear force and accumulation of plastic strain.This study provides a theoretical reference for the manufacture of high-strength aluminum alloy fasteners through composite deformation and helps improve processing technology.