27.12.2013 Views

COST 507 - Repositório Aberto da Universidade do Porto

COST 507 - Repositório Aberto da Universidade do Porto

COST 507 - Repositório Aberto da Universidade do Porto

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

GR2<br />

Differential Scanning Calorimetry and Thermodynamic<br />

Calculations aimed at the Development of Al-Mg-Si Cast<br />

Alloys with Cu, Ag and Sm Additions<br />

G. N. Haidemenopoulos and A. N. Vasilakos<br />

Department of Mechanical and Industrial Engineering,<br />

University of Thessaly, Volos, Greece<br />

Abstract<br />

This work has been performed within the framework of <strong>COST</strong> <strong>507</strong> Round II<br />

program on the Al-Mg-Si-Cu system (Leading system 2). DSC measurements<br />

have been performed on three alloys based on the conventional A357<br />

composition with additions of Cu, Ag and Sm. For the three alloys, designated<br />

A357+CU, A357+Cu+Ag, and A357+Cu+Sm, the solidification regimes as well<br />

as the transformation enthalpies for melting and solidification were determined.<br />

The results were compared with predictions of the thermochemical <strong>da</strong>tabase<br />

and software system Thermo-Calc. Additional thermodynamic calculations<br />

included isopleth sections and Scheil solidification diagrams showing the<br />

development of microsegragation. Calculation of the precipitation driving forces<br />

for the strengthening phases Mg 2 Si and AI 2 Cu were conducted as a function of<br />

alloy composition and ageing temperature. These calculations established the<br />

recommended ageing temperatures of the alloys. Application of the modified<br />

ageing treatments (relative to the conventional A357 alloy) resulted in<br />

improved combinations of strength and ductility.<br />

1. Introduction<br />

Aluminum alloy A357, which is based on the Al-Mg-Si system, is widely used in<br />

precision casting applications. The effect of several alloying elements in A357<br />

has been studied e.g. Be additions [89Bru, 83Nag, 84Gra], La additions<br />

[83Bac], as well as Na, Sr and Sb additions [880ze, 86Mai, 89Ape]. It has<br />

been proposed [96Bri] that combined additions of Cu with Ag and Sm could<br />

lead to further enhancement in strength and ductility of precision cast alloy<br />

A357. The present work was conducted in the framework of <strong>COST</strong> <strong>507</strong> Round<br />

II program in order to investigate additions of Cu, Ag and Sm to the<br />

conventional alloy A357. Differential Scanning Calorimetry (DSC) was<br />

employed to determine the melting and solidification regimes as well as the<br />

enthalpies for melting and solidification. The results were then compared with<br />

the predictions of the thermochemical <strong>da</strong>tabase and software program<br />

Thermo-Calc. Further calculations were targeted towards improving the ageing<br />

treatment of the alloys.<br />

- 139

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!