Thermodynamic evaluation of the thixoformability of Al-Si-Cu alloys

Author(s)

Brollo, Gabriela Lujan ^[1] ; Tarnayo, Daimer Velazquez ^{[1, 2]} ; Torres, Luis Vanderlei ^[3] ; Zoqui, Eugenio Jose ^[1]

Affiliation

^[1] Univ Estadual Campinas, UNICAMP, Sch Mech Engn, Mat & Mfg Dept, BR-13083860 Campinas, SP - Brazil

^[2] UO, Sch Mech Engn, Santiago De Cuba - Cuba

^[3] IFSP, Fed Inst Educ Sci & Technol Sao Paulo, BR-12903000 Braganca Paulista, SP - Brazil

• Document type: Journal article
• Source: CALPHAD-COMPUTER COUPLING OF PHASE DIAGRAMS AND THERMOCHEMISTRY; v. 67, DEC 2019.
• Web of Science Citations: 1

Abstract

The aim of this work was to evaluate the thixoformability of Al-(2 to 7 wt%) Si-Cu alloys by differential thermal analysis (DTA), differential scanning calorimetry (DSC) and CALPHAD simulation. Thermoanalytical data were generated for exothermic (rheocasting) and endothermic (thixoforming) cycles under different kinetic conditions (heating and cooling rates of 5, 10, 15, 20 and 25 degrees C/min). The findings indicate that the SSM critical temperatures and liquid fractions are directly affected by the kinetic conditions, chemical composition and heat-flow direction and that the measured values of these critical temperatures and liquid fractions vary according to the thermodynamic evaluation technique used (Calphad simulation, DSC or DTA). The SSM working window (a) became smaller as the heating/cooling rates and Si content increased; (b) was larger for rheocasting (solidification) than for thixoforming (melting) operations; (c) was on average approximately 12 degrees C wider and covered a range of mass fractions approximately 0.12 greater for DSC measurements than for DTA measurements; and (d) had a low sensitivity for all the conditions analyzed, indicating the thermodynamic stability of the Al-Si-Cu system. CALPHAD simulation successfully predicted several transformations and the thermodynamic behavior of the temperatures and liquid fractions analyzed. The DTA and DSC techniques yielded discrepant results for some of the critical points investigated, such as the limits of the SSM working window. The majority of the DSC cycles were more sensitive to variations in kinetic conditions, heat-flow direction and chemical composition than the corresponding DTA cycles. Furthermore, the tertiary Al2Cu phase transformation could not be identified in many of the DTA cycles. For these reasons, DTA should be used with caution when predicting the thermodynamic behavior of potential raw materials for SSM processing. (AU)

• FAPESP's process: 09/08478-1 - Continuous Casting and Thixoforming of new Al-Si-Cu-Mg alloys
• Grantee: Luis Vanderlei Torres
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 15/22143-3 - Fatigue behaviour of thixoformed alloys
• Grantee: Eugênio José Zoqui
• Support Opportunities: Regular Research Grants
• FAPESP's process: 13/09961-3 - Upgrade of the Foundry and Thixoforming Laboratory at FEM/Unicamp
• Grantee: Eugênio José Zoqui
• Support Opportunities: Regular Research Grants