The precipitation evolution and mechanical properties of a commercial Al-Cu-Li-Mg alloy in natural aging(NA)tempers(T3 and T4)were investigated in detail.It was demonstrated that GPI zones were the pre-dominant precip...The precipitation evolution and mechanical properties of a commercial Al-Cu-Li-Mg alloy in natural aging(NA)tempers(T3 and T4)were investigated in detail.It was demonstrated that GPI zones were the pre-dominant precipitate throughout the NA process.In the T3-aged sample,the precipitation sequence was determined:supersaturated solid solution(SSSS)→atom clusters→GPI zones,whereas in the T4-aged sample,it was SSSS→atom clusters→GPI zones→GPI zones+δ/GPI zones/δ.For samples without NA,the strength of the T3 sample was 76.0 MPa higher than that in the T4 sample,which was attributed to the pre-deformation-introduced dislocations.During the early stage of NA,GPI zone nucleation was substantially restricted in the T3 sample,resulting in a much lower number density of GPI zones.It re-tarded the aging response and strength improvement,consequently narrowing the strength difference between T3 and T4 samples.As the NA process progressed,the average diameter of GPI zones in the T4 sample increased to approximately 4.5 nm,accompanied by the formation ofδ/GPI zones/δcomposite precipitate.However,GPI zone growth andδ/GPI zones/δcomposite precipitate formation were signifi-cantly inhibited in the T3 sample,as evidenced by its much smaller average diameter of approximately 2.1 nm and the absence of composite precipitates.It inhibited the strength improvement of the T3 sam-ple.Therefore,after a long period(5 months)of NA,the strength of the T4 sample was about 13.0 MPa higher than that of the T3 samples,instead.展开更多
The microstructure and mechanical properties of as-cast Al−Cu−Li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated.Experime...The microstructure and mechanical properties of as-cast Al−Cu−Li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated.Experimental results demonstrated that compared with the gravity casting technique,the water-cooling centrifugal casting technique significantly reduces porosity,refinesα(Al)grains and secondary phases,modifies the morphology of secondary phases,and mitigates both macro-and micro-segregation.These improvements arise from the synergistic effects of the vigorous backflow,centrifugal field,vibration and rapid solidification.Porosity and coarse plate-like Al13Fe4/Al7Cu2Fe phase result in the fracture before the gravity-cast alloy reaches the yield point.The centrifugal-cast alloy,however,exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%.This high yield strength is attributed to solid solution strengthening(SSS)of 225.3 MPa,and grain boundary strengthening(GBS)of 35.7 MPa.Li contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^(-1).The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior,refining the microstructure and changing the morphology of secondary phases.展开更多
文摘The precipitation evolution and mechanical properties of a commercial Al-Cu-Li-Mg alloy in natural aging(NA)tempers(T3 and T4)were investigated in detail.It was demonstrated that GPI zones were the pre-dominant precipitate throughout the NA process.In the T3-aged sample,the precipitation sequence was determined:supersaturated solid solution(SSSS)→atom clusters→GPI zones,whereas in the T4-aged sample,it was SSSS→atom clusters→GPI zones→GPI zones+δ/GPI zones/δ.For samples without NA,the strength of the T3 sample was 76.0 MPa higher than that in the T4 sample,which was attributed to the pre-deformation-introduced dislocations.During the early stage of NA,GPI zone nucleation was substantially restricted in the T3 sample,resulting in a much lower number density of GPI zones.It re-tarded the aging response and strength improvement,consequently narrowing the strength difference between T3 and T4 samples.As the NA process progressed,the average diameter of GPI zones in the T4 sample increased to approximately 4.5 nm,accompanied by the formation ofδ/GPI zones/δcomposite precipitate.However,GPI zone growth andδ/GPI zones/δcomposite precipitate formation were signifi-cantly inhibited in the T3 sample,as evidenced by its much smaller average diameter of approximately 2.1 nm and the absence of composite precipitates.It inhibited the strength improvement of the T3 sam-ple.Therefore,after a long period(5 months)of NA,the strength of the T4 sample was about 13.0 MPa higher than that of the T3 samples,instead.
基金support from the National Science Foundation of China (No.51971249)the Natural Science Foundation of Shandong Province,China (No.ZR2020KE012)the Science and Technology Planning Project of Longkou City,China (No.2021KJJH025).
基金financially supported by the Natural Science Foundation of Ningbo,China (No.2023J053)。
文摘The microstructure and mechanical properties of as-cast Al−Cu−Li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated.Experimental results demonstrated that compared with the gravity casting technique,the water-cooling centrifugal casting technique significantly reduces porosity,refinesα(Al)grains and secondary phases,modifies the morphology of secondary phases,and mitigates both macro-and micro-segregation.These improvements arise from the synergistic effects of the vigorous backflow,centrifugal field,vibration and rapid solidification.Porosity and coarse plate-like Al13Fe4/Al7Cu2Fe phase result in the fracture before the gravity-cast alloy reaches the yield point.The centrifugal-cast alloy,however,exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%.This high yield strength is attributed to solid solution strengthening(SSS)of 225.3 MPa,and grain boundary strengthening(GBS)of 35.7 MPa.Li contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^(-1).The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior,refining the microstructure and changing the morphology of secondary phases.
