Effect of Sr-P Interaction on the Microstructure and Tensile Properties of A413.0 Type Alloys

A M Samuel,H W Doty,F H Samuel,S Valtierra

doi:10.1155/2016/7691535

A M Samuel, H W Doty + Show 2 more

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https://doi.org/10.1155/2016/7691535

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Abstract

The present study was performed on low magnesium A413.0 type alloys. The results show that strontium (Sr) is mainly concentrated in the silicon particles. Overmodification occurs when Sr precipitates in the form of Al2SrSi2, which takes place over a wide range of temperatures. The first peak occurs following the precipitation ofα-Al, the second peak is merged with the precipitation of eutectic silicon (Si), and the third peak is a posteutectic reaction. Introduction of phosphorus (P) to Sr-modified alloys leads to the formation of (Al,P,Sr)2O5compound, which reduces the modification effectiveness of Sr. Therefore, in the presence of P, the amount of added Sr should exceed 200 ppm. For the same levels of P, the tensile parameters of well modified alloys (233 ppm Sr) are relatively higher than those partially modified with Sr (about 60 ppm Sr) containing the same amount of P. During solution heat treatment, coarsening of the eutectic Si particles occurs by the growth of some particles at the expense of the dissolution of the smaller ones, as well as by the collision of nearby particles.

Highlights

The mechanical properties of Al-Si alloys strongly depend on many factors including chemical composition, molten metal processing and casting techniques, heat treatment, and microstructure, in particular the morphology of the eutectic silicon
The results show that strontium (Sr) is mainly concentrated in the silicon particles
The associated wavelength dispersive spectroscopic (WDS) analysis (Table 3) reveals that these spots are a mixture of different oxides, mainly Al2O3 and AlPSrO, as confirmed by the X-ray images showing the element distribution within the black spots

Summary

Introduction

The mechanical properties of Al-Si alloys strongly depend on many factors including chemical composition, molten metal processing and casting techniques, heat treatment, and microstructure, in particular the morphology of the eutectic silicon. In the normal as cast condition, the eutectic Si particles occur as brittle acicular flakes in the microstructure. Such acicular particles act as crack initiators and provide easy paths for fracture and, reduce the mechanical properties of the alloy [1]. Groups IA and IIA elements are well known to act as effective modifiers in Al-Si alloys where, with the addition of elements like Ca, Na, Sr, and Sb, the morphology of the eutectic Si particles can be altered to a fine lamellar or fibrous eutectic network. The most acceptable explanation of the change in the eutectic Si morphology suggests that the growth of silicon particles within the eutectic regions is prevented by the addition of such modifiers [2,3,4,5]

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Conclusion