| 7050alloy, which belongs to Al-Zn-Mg-Cu series, is a high-strength aluminumalloy. It is widely used in the fields of aviation and astronautics. With thedevelopment of current technology, aluminum alloys are demanded to have moresuperior mechanical properties, especially fatigue and fracture properties. Therefore,studying how to further improve the mechanical properties of high-strengthaluminum alloys is a worthwhile work. The author of this paper prepared7050alloys with various Sc contents by adding trace amounts of Sc to7050alloy, andthen studied the effects of Sc on age-hardening behavior, axial high cycle fatigueperformance, fatigue crack initiation resistance and growth rate and fracturetoughness of7050alloy. The main research contents and results are as follows:(1) The effects of single-and two-stage solid solution treatment on theage-hardening behavior of as-cast7050alloy with Sc addition were investigated.The results showed that when using single-stage solution treatment,7050alloys withand with no Sc addition, which were treated with solution-treatment at470℃for1hour and then aging at120℃, all could get higher peak hardness when comparingwith the alloys solution-treated at460℃o r480℃. So,470℃was a reasonabletemperature for solid solution treatment of7050alloy with Sc addition. Sc contenthad little influence on the age-hardening behavior of7050alloys with Sc additionwhen they were solution-treated at460℃. But,7050alloys with higher Sc contentcould achieve a higher peak hardness when they were solution-treated at470℃or480℃; When using two-stage solution treatment, there were no obvious changes thatcould be observed in the age-hardening behavior of7050alloys with Sc addition,and it basically identical to that of the single-stage solid solution-treated alloys.(2) The axial high cycle fatigue performance of7050alloys with Sc additionwere investigated. The results revealed that the fatigue performance of7050alloyswith Sc addition was visibly better than that of7050alloy with no Sc addition. Thus,Sc addition could improve the high cycle fatigue performance of7050alloy. Sccontent had some influence on the fatigue performance of7050alloys with Sc addition. The best fatigue performance could be achieved when Sc content was0.252%.. However, the fatigue performance of the alloy declined when Sc contentwas increased up to0.484%. It suggested that excessive Sc content could notimprove the high cycle fatigue performance of7050alloy.(3) The effects of Sc on the fatigue crack initiation resistance and fatigue crackgrowth behavior of7050alloy were investigated. The results indicated that fatiguecrack initiation life of the alloy samples first rose and then dropped with the increaseof Sc content of the alloys, and the alloy sample would have the best fatigue crackinitiation resistance when Sc content was0.252%. The results of fatigue crackgrowth tests for7050alloys with Sc addition showed that the7050alloys with0.252%Sc addition exhibited the best fatigue crack growth resistance under the testcondition of stress ratio R=0.1. But, when the tests were carried out under the testcondition of stress ratio R=0.5, the fatigue crack growth resistance of the7050alloywith0.484%Sc addition was the best. Thus it can be seen that the effect of Sc on thefatigue crack growth behavior of7050alloy is irregular. It needs further research.(4) The fracture toughness of7050alloys with Sc addition was studied. Theresults revealed that the strength ratio of7050alloys with Sc addition rose with theincrease of the Sc content of the alloy, and the strength ratio of the alloy was thehighest when Sc was0.252%, accordingly, the alloy should have the highest fracturetoughness. However, the fracture toughness of the alloys would drop if more Sccontent was added to7050alloy.In conclusion, the best efficiency can be achieved when adding0.25wt%Sc to7050alloy for improving the fatigue performance and fracture toughness of the alloy.So, it is an ideal amount of Sc addition for7050alloy. |
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