CAJ | 학술논문

在等效应变幅为0.22%时,研究了Al-7Si-0.3Mg铸造铝合金在比例、圆形.正方形,菱形,矩形与椭圆形路径下的循环变形行为,并用TEM观察了疲劳失效试样的位错结构.结果表明:在多轴加载条件下,材料均表现出循环硬化现象,循环硬化的速率和程度对加载路径有依赖性;非比例载荷下材料的疲劳寿命远小于比例加载时的寿命,且非比例加载下的疲劳寿命对各种非比例加载路径有依赖性,其中圆形路径下疲劳寿命最短;位错在不同的加载路径下形成不同的组态结构,位错与强化相、枝晶界及位错问的交互作用是铸造铝合金发生循环硬化的主要原因.
재등효응변폭위0.22%시,연구료Al-7Si-0.3Mg주조려합금재비례、원형.정방형,릉형,구형여타원형로경하적순배변형행위,병용TEM관찰료피로실효시양적위착결구.결과표명:재다축가재조건하,재료균표현출순배경화현상,순배경화적속솔화정도대가재로경유의뢰성;비비례재하하재료적피로수명원소우비례가재시적수명,차비비례가재하적피로수명대각충비비례가재로경유의뢰성,기중원형로경하피로수명최단;위착재불동적가재로경하형성불동적조태결구,위착여강화상、지정계급위착문적교호작용시주조려합금발생순배경화적주요원인.
Widely application of cast aluminum alloy requires an understanding of its cyclicdeformation behavior which is material dependent,and it is a complex function of strain amplitude,loading path,etc.In this study,multi-axial fatigue tests were conducted on cast Al-7Si-0.3Mg alloy with the same equivalent strain amplitude of 0.22%under six multi-aXial path loadings,whjch were proportional,circular,square,diamond,rectangle and ellipse paths.TEM was employed to investigate the dislocation structures of the fatigue failure specimens.Cyclic hardening dominates the whole fatigueprocess under every loading path,but the rate and extent of cyclic hardening are quite dependent on particular loading paths.The fatigue life under nonproportional loading is much lower than that under proportional loading,and it also depends on the various nonproportional loading paths.The specimen with circular path loading has the shortest life and the most severe cyclic hardening among all the loading paths.The continuously changing of direction of maximum shear-stress plane is attributedto the complicated dislocation substructures and severe stress concentration during the cyclic process-The interaction among dislocation,particle and cell boundary is the main reason for cyclic hardening.The structure and density of dislocation in fatigue failure specimens under various loading paths exhibit quite different.From double dislocation bands,multiple dislocation bands,labyrinth structure to cell structure.the dislocation mobility decreases and stress concentration degree increases.KEY WoRDS Al-7Si-0.3Mg alloy,nonproportional loading,multi-axial fatigue,dislocation