利用室温单向拉伸实验、EBSD和TEM等手段,研究了柱状晶组织HA177-2铝黄铜的力学性能与加工硬化行为,探讨了晶粒尺寸对拉伸变形加工硬化速率和塑性变形能力的影响及其机制.结果表明,柱状晶组织HA177-2铝黄铜加工硬化速率-真应变关系曲线第2阶段具有显著上升趋势,晶内形成平行分布的小角度亚晶界使位错滑移长度减小并阻碍位错运动是加工硬化速率上升的主要原因,不同于文献报道的等轴晶组织黄铜加工硬化第2阶段形成形变孪晶使滑移长度减小的机制.随着晶粒尺寸的增大,柱状晶组织HA177-2铝黄铜的屈服强度和抗拉强度降低,而断后伸长率显著增大,由晶粒尺寸为2.0 mm的70.4％增大到晶粒尺寸为6.0 mm的84.4％.较高的抗塑性失稳能力和较好的晶内变形均匀性是大晶粒柱状晶试样具有更优塑性变形能力的主要原因.
The mechanical properties and work hardening behavior of columnar-grained HA177-2 brass were investigated by means of room temperature tensile test,EBSD and TEM.The effects of grain size on the work hardening rate and tensile ductility of the alloy were discussed.Some references reported that deformation twinning developed in the equiaxed-grained brass led to a reduction in slip length of dislocation and an increase in the work hardening rate at the second stage in the curve of work-hardening vs strain.In this work,however,the results showed that the low-angle subgrain boundaries distributed parallelly were formed in the columnar grain and reduced the slip length of dislocation at the second stage,which was responsible for the rise of the work hardening rate.With increasing grain size,both the yield strength and ultimate tensile strength of the columnar-grained HA177-2 brass decreased,but its elongation to failure increased significantly from 70.4％ for the grain size of 2.0 mm to 84.4％ for the grain size of 6.0 mm.Higher performance to resist the plastic instability and better deformation uniformity mainly contributed to the ductility improvement of the larger-grain-sized columnar-grained HA177-2 brass.
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