摘要:
建立了搅拌摩擦焊铝合金接头焊核区等轴再结晶组织形成过程的物理模型,详细阐述了焊核区的组织形成过程。试验结果表明,热循环的作用导致搅拌头附近的母材发生软化,形成软化层;软化层在搅拌头的机械搅拌作用下发生塑性流动,软化层内不同的流层间流速不同,存在速度梯度。在流层间的界面处产生粘性摩擦剪应力。在粘性剪应力的作用下,母材轧制态下的板条状组织被拉长,并发生强烈的弯曲变形,当弯曲程度超过了其晶界所能承受的上限时,原有的板条状组织晶界被破坏而逐渐消失,板条内的等轴再结晶组织按能量最小原理重新排列,形成焊态下无序、无方向性的等轴再结晶组织排列。
Abstract:
A physical model of the forming process of equiaxed grain in weld nugget zone during friction stir welding of aluminum alloy was established.Experimental results showed that thermal cycle caused material softening near rotation tool.Softening material flowed as plastic state under the mechanical stir of rotation tool.The speed of different flowing layer in softening material was different,resulting in speed gradiends and sticking friction shear stress at the interface between adjacent layers.Under the shear stress,the banded structures of parent material were highly elongated and bended.When the degree of bend exceeded the limit of grain boundary,the original banded structures boundary began to degrade,and the equiaxed grains forming in banded structures were arrayed by the energy principle,resulting in no order and direction pattern of equiaxed grains.
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