多目标质量的粉末包套等通道挤扭成形致密工艺参数优化

Optimization of Forming and Densification for Al Powder in Tubes-equal Channel Twist Extrusion Based on Multi-objective Quality

剧烈塑性变形法—挤扭以剪切塑变为主变形方式,成形工艺复杂,影响因素很多,难以精确地建立工艺参数与成形质量之间的关系;选取优化合理的工艺参数匹配是材料尤其是粉末材料成形无破裂、塑性好、致密化程度高等成形质量的关键。以等通道横截面扭转角、螺旋角、摩擦因子、挤压速度、初始相对密度为自变量,正交试验为设计方案,对纯铝粉末烧结材料进行一道次包套等通道扭挤数值模拟,获得以等效塑性应变、静水压力、最大损伤值、相对密度数据,通过层次分析法计算多质量目标的权重,运用追踪点法和灰色系统理论的灰色关联度优化工艺参数,使设计目标值达到等效应变最大、静水压力最大、最大损伤值最小、相对密度最大。模拟和试验结果表明,运用多目标优化组合参数进行等通道挤扭成形能使纯铝粉末体材料迅速地形变累积,静水压力提高,损伤值显著地减小,致密效率高,晶粒明显细化,提高了材料综合质量。

As a new severe plastic deformation method（SPD）,twist extrusion（TE）is a complex forming process because of the main shear plastic deformation and many factors affecting;and it is difficult to accurately establish the relationship between process parameters and the forming quality.Selecting optimized rational process parameters matching is the key to acquire quality i.e.fine plastic and dense,no rupture for materials forming especially powder materials.The finite element simulation about pure aluminum powder in tubes-twist extrusion is carried out by Deform-3D software after the establishment of orthogonal experimental design to the factors about the cross-section torsion angle,helix angle,the friction factor,extrusion speed,the initial relative density.The average equivalent plastic strain,hydrostatic pressure,the average maximum damage value and the average relative density as the optimization design goal and process parameters are optimized by means of track-point method and gray system theory before the weight of multi-object is calculated by analytic hierarchy process.Ultimately it is achieved that there have maximum of equivalent strain,maximum of hydrostatic pressure,minimum of the maximum damage value,maximum of relative density.Results of simulation and experimental validation show that twist extrusion used of multi-objective optimization of parameters makes value of the effective strain and hydrostatic pressure accumulated rapidly,the maximum damage significantly reduced,dense significant and grain refinement obtained,and comprehensive and good quality materials obtained too.