Application Of Y And CNTs In ADC12 Alloys And Their Performances

ADC12 aluminum alloy belongs to Al-Si-Cu alloy,and the specific strength is high,the thermal expansion coefficient is small,the corrosion resistance and thermal conductivity is excellent.And the casting properties are excellent,but the ?-Al phase of the as-cast ADC12 alloy is coarse,the eutectic silicon phase shows coarse plate-like,and the iron-rich phase shows thick and long needle,which resulting the low mechanical properties and the limit of the use of ADC12 aluminum alloy.The application and properties of rare earth Y and CNTs in ADC12 aluminum alloy were studied in this study.The results showed that the addition of Y significantly refined the ?-Al phase and ?-Fe phase and modified eutectic silicon(Si)phase of ADC12 alloys.When the addition of Y is 0.2 wt%,the secondary dendritic arm spacing(SDAS)(6.9 ?m)is decreased by 75.6% when compared with unmodified ADC12 alloy.The eutectic Si phase was fully modified into fine fibrous and granular structure,and the sharp corners disappeared,the average area and aspect ratio decreased to 1.7 ?m2 and 1.9,which were increased by 96.1% and 89.0% as compared to unmodified ADC12 alloy respectively.The length of ?-Fe phase(3.1 ?m)is decreased by 85.8% as compared to the unmodified alloy.The UTS(255.62 MPa),elongation(3.25%)and hardness(94.6 HV)were increased by 48.3%,72.9% and 24.6% as compared with unmodified alloys respectively.When the addition of Y is more than 0.3 wt%,the ?-Al phase,eutectic silicon phase and ?-Fe phase begins to coarsen.For the 0.2 wt% Y modified ADC12 alloy,the suitable solution temperature is 520 °C,the eutectic silicon phase was fully spheroidized,the sharp corners of the ?-Fe phase disappeared,which improved the mechanical properties of the alloys.When the solution temperature is 500 °C,the eutectic silicon phase was fully spheroidized,but the sharp corners of ?-Fe phase were not disappeared.When the solution temperature is 540 °C,over-heated was produced in the alloy,some eutectic Si phase and iron-rich phase were coarsened,and the others of eutectic silicon phase and iron-rich phase showed raindrops,which distribution in the alloy grain boundary with Cu-rich phase.When Y was addition into the ADC12 alloy,the eutectic Si phase was refined and the size was uniform.The iron-rich phase was also refined and the Al2 Cu phase was fully dissolved in the matrix.The tensile strength(313.51MPa),the elongation(3.19%)and the hardness(132.7%)of the alloy were obtained after quenching and artificially aging(170 °C for 10h),which were increased by 81.89%,70.59% and 74.31% as compared to the ADC12 alloys without heat treatment.High-intensity ultrasonic treatment is more effective to disperse the CNTs into ADC12 matrix than mechanical string.For the 1.0 wt% CNTs/ADC12 composite fabricated by High-intensity ultrasonic treatment,the eutectic Si phase changes from coarse needle to granular as the addition of CNTs.When the addition of CNTs was 1.0 wt%,the UTS(251.91 MPa)and hardness(103.34 HV)were increased by 27.0% and 29.5% as compared to the unreinforced ADC12 alloys.When the addition of CNTs is greater than 1.0 wt%,the CNTs begin to agglomerate.The fracture analysis confirmed that the high-intensity ultrasonic treatment was more effective to disperse the CNTs into matrix than mechanical stirring.TEM analysis results showed that the wettability between CNTs and aluminum alloy was improved,and the reaction between CNTs and aluminum alloy matrix was suppressed by high-intensity ultrasonic treatment.