| Squeeze Casting is an advanced near-net-shape forming technology which combined thecharacteristics of casting forming and plastic forming. Al-Cu alloys is a high-strength andhigh-ductility aluminum alloys prepared by squeeze casting, which can be used in aviation,aerospace, defense and other important areas for lightweighting equipments. As so far, theresearch on static mechanical properties of Al-Cu alloys prepared by squeeze casting wasmainly focused on the methods of the optimization of process parameters and alloycompositions, but the dynamic mechanical properties got less attentions relatively. The lowcycle fatigue test is widely used in the field of fatigue research areas because of itscost-effective and data-centraliaed. In this paper, the low cycle fatigue behavior of analuminum alloys prepared by squeeze casting in cast and heat treatment states, mainly consistof5.0wt%Cu0.4wt%Mn, and a comparative study with A356alloy carried out by means ofthe low cycle fatigue test and methods of metallographic analysis, SEM, TEM. Theconclusions in the article are as follows:(1) Al-5.0Cu-0.4Mn alloys with different pressure showed obvious continuous cyclichardening behavior, cyclic stress response curve grossly corresponds to three stages of thealloy fracture process, the alloy cyclic stress and total strain amplitude have directly relationswhich adapt to the Hollomon equation. As the pressure increases, the cyclic stress responsecurve begins showing the "saturation" and "instability" stage, and the maximum strengtheningalso increases. The general cycle number significantly gets longer and a long period of cycle"steady state" appeared after alloy in T5heat treatment.The study of the intrinsic relationshipbetween dislocation state changes and low cycle fatigue cyclic hardening indicate that theinteraction between dislocation and dislocation, and between dislocation and the second phaseproduced cyclic hardening.(2) The research on the effect on low cycle fatigue life of pressure and T5heat treatmentby means of metallographic analysis SEM TEM. Results showed that pressure and T5heattreatment can significantly improve the low cycle fatigue life of the Al-5.0Cu-0.4Mn alloybecause the former greatly reduced the number of fatigue source and after heat treatment of alarge number of dispersed T’’ and secondary T phase are precipitated. The low cycle fatiguelife curve of the alloy with different pressure and states (cast and heat treatment) accord withthe Manson-Coffin and Basquin relationship, the Basquin equation can create stress-liferelationship which can be used to forecast fatigue life under the control of stress. As cast,Al-5.0Cu-0.4Mn exist transitional fatigue life and move right by greater pressure, after heat treatment there is no obvious transitional fatigue life due to the high strength and elasticmodulus increases.(3) Plastic strain energy density of Al-5.0Cu-0.4Mn alloy prepared by squeeze castingreduced with the increase of cycle times and is related to cyclic strain amplitude in directproportion,’Wp-2Nfrelationships accord with the Halford-Marrow equation.(4) The law of cyclic hardening behavior of A356alloy in cast and heat treatmentprepared by squeeze casting cast is the same as the law of Al-5.0Cu-0.4Mn alloy. Low cyclefatigue life of A356alloy also increased with pressure and T6heat treatment, but the pressurehad a more significant effect on Al-5.0Cu-0.4Mn alloy. Low cycle fatigue life ofAl-5.0Cu-0.4Mn alloy was obviously longer than the A356alloy. A356alloy also existstransitional fatigue life and changes little with pressure and heat treatment. Plastic strainenergy density of A356alloy prepared by squeeze casting reduced with the increase of cycletimes and is related to cyclic strain amplitude in direct proportion, and A356alloy got biggerplastic strain energy density and shorter life than Al-5.0Cu-0.4Mn alloy. |
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