Comparison of the Porosity of Aluminum Alloys Castings Produced by Squeeze Casting

Abstract

The results of researches on porosity and structure of castings from AlMg9, AlSi7Mg and AlCu4Ti alloys produced by squeeze casting and for comparison by gravity die casting are presented. The tests were carried out on 200x100x25mm plates squeeze casted under 90MPa pressure. Prior to the commencement of experimental studies, numerical simulations of solidification were made for the selected alloy (AlSi7Mg) in order to determine the potential locations of shrinkage porosity. As part of the study, the porosity distribution in the plate cast was assessed by taking samples for measurements from the center and edge of the casting. It was found that the area particularly vulnerable to the presence of shrinkage porosity is the central part of the casting and the zone extending from its center to the upper surface. Due to the wide temperature range of solidification of the examined alloys, diffused porosity occurs in castings, and the shape of the pores formed is conditioned on the solidification morphology. The average porosity of squeeze castings is two times smaller than gravity die castings and is at the level of 1.0-1.5% depending on the type of alloy. In addition, as a result of pressing, the shrinkage porosity in the central part of the plate is reduced and its distribution becomes uniform throughout the volume. High pressure acting on solidifying castings ensures a significant increase of grains density in microstructure and decrease of SDAS.

Joining Technologies for Aluminium Castings—A Review

“…Once the cavity is full, a pressure is added to the melt to over 100 MPa and held to compensate for shrinkage until the casting has solidified [10]. Zyska and Boro ń [14] compared the porosity of three aluminium castings, AlMg9, AlSi7Mg, and AlCu4Ti, made by gravity die casting and squeeze casting. The results showed that the porosity in the castings made by squeeze casting was almost half that of the castings made by gravity die casting.…”