Alternative Modification of A356 Hypoeutectic Alloy by Ca-Si-Ba Additions" Alexandre Bois-Brochu and Marin Gheorghe, Centre de Metallurgie du Quebec, Trois-Rivieres, Quebec, Canada; Francis Breton, Rio Tinto, Arvida Research and Development Centre, Ontario, Canada
This chemical modification is used for Al-Si hypoeutectic alloys.
Consideration is given to the solidification of a typical hypoeutectic alloy
, containing 7% silicon.
Figure 1b shows regularly-shaped graphite flakes in a hypoeutectic alloy
with high C content.
14], the nucleation of Si during the solidification of Al-Si hypoeutectic alloys
appears to result from a hierarchy of nucleating substrates operating at progressively lower temperatures: (1) AlP, whose generally particulate morphology can initiate the formation of compact Si particles as seen in hypereutectic alloys, (2) oxide bifilms alone, whose planar form creates plate-like Si morphologies, and (3) a currently unknown nucleant that initiates the coral eutectic growth morphology.
It was realized that, to have the thixoforming process of these hypoeutectic alloys
correctly applied, it is necessary to achieve a temperature where AlFCC coexists with the liquid rich-silicon; nevertheless, the semisolid behaviour will depend on the remaining solid's morphology and shape.
As part of a larger program to establish statistically validated mechanical properties for E357-T6 sand castings, this weld repair study was designed to consolidate industry best practices to establish an AFS Recommended Practice for the in-process weld repair of aluminum-silicon hypoeutectic alloys
, develop mechanical properties to demonstrate the efficacy of the practice, and develop statistical data that facilitates acceptance of the weld practice.
The research team will develop a practice for in-process weld repair of aluminum-silicon hypoeutectic alloys
, track the mechanical properties to demonstrate the effectiveness of the practice and provide a statistical basis for acceptance.
For hypoeutectic alloys
, liquidus (TL) should have a well-defined plateau indicating dendritic growth.
In aluminum-silicon (Al-Si) hypoeutectic alloys
, strontium is often added for modification of the Si structure during the alloying process.