Impact Of Hot Isostatic Pressing On Aluminum Casting Alloy E357

Open Access
Author:
Pathak, Abhishek Sanjay
Graduate Program:
Industrial Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Robert Carl Voigt, Thesis Advisor
Keywords:
  • Hot Isostatic Pressing
  • E357
  • Cast alloy
  • microporsity
  • size of silicon particle
Abstract:
Ductile materials such as aluminum alloys have been the primary material of choice for structural components of aircraft such as fuselage, wing, etc. because of their light weight, ease of forming and resistance to failure under shock loads. There are two primary types of aluminum alloys used in aircraft: cast alloys and wrought alloys. Majority of the traditionally used cast aluminum alloys in aircraft manufacturing are the Al-Cu or Al-Si-Mg alloys including A214, A355, A356 and E 357. Aluminum castings are typically produced using green sand, permanent mold casting or die casting. However, aluminum castings are susceptible to porosity defects. Porosity is a microscopic void or hole found in a casting. To eliminate micro-porosity defects in aluminum castings, multiple heat treatments can be used. In particular hot isostatic pressing (HIP) can be used to effectively to remove sub-surface porosity in complex shaped castings. HIPing process includes the use of elevated temperature and the application of a hydrostatic pressure via pressurized gas. Previous work has demonstrated that widely used aluminum casting alloys such as A356, A204, A206 have shown considerable improvement in mechanical properties when HIPed. However, no study has been done on aluminum casting alloy E357. The E357 alloy combines excellent casting characteristics with improved strength compared to the widely use A356 alloy. Silicon combines with the magnesium in these alloys to form Mg2Si which strengthens the alloys during final precipitation heat treatments. To understand the effects of hot isostatic pressing on the performance of casting Aluminum E 357 alloy tensile testing and charpy impact testing were carried out on cast E357 test specimens which were divided into three groups- HIPed and T6 heat treated specimens,Homogenized and T6 heat treated specimens and Non HIPed and T6 heat treated specimens. Samples were evaluated to understand the effects of processing cycles on the resultant mechanical properties and microstructure with respect to microporosity and size of silicon particles. This study was conducted as an effort to characterize impact of Hot Isostaic Pressing on aluminum E357 casting for Sikorsky Aircraft Corporation. It was observed that, HIPing process helped in reducing %porosity by 37.83% and increased size of silicon particle has by 18.08%. Significant increase in %elongation was also observed in HIPed samples as compared to non HIPed samples. Overall HIPing process and subsequent heat treatment helps to improve % elongation significantly although the improvements in ultimate tensile strength and yield strength is not significant. Microstructure analysis reveals that HIPing results in a noticeable reduction in % porosity which tends to increase mechanical properties and reduce property variation.