MS Thesis: Improvement in Impact Strength and Fracture Toughness of Castings through Chemically Induced Surface Residual Stress

Tuesday, December 18, 2018
10:00 am
Floor/Room #: 


Alloys with good fracture toughness and elevated temperature properties like A201 are expensive and can be more difficult to process. This results in the use of heavier but less expensive alternatives in many applications where toughness is of concern, such as steels. Common alloys such as A356 and E357 are relatively cheap and easy to work with. However, these alloys have considerably lower fracture toughness than premium alloys. This research aims to investigate surface modification treatments that could yield better fracture toughness at a low cost in a common aluminum alloy. The process must show significant improvement in said properties, be cost effective, and easily adaptable in a common foundry. Methods for inducing compressive residual stresses in the surface were explored by means of coating and tempering aluminum parts. Diffusion of coating material into the substrate was investigated with a variety of coating metals. The diffusion process was facilitated in the solutionizing step for the given substrate aluminum in order to strengthen the sub-surface region of the parts. This research aims to provide a platform for further research into the practical effects of the coating and tempering on impact and fracture properties. These samples were characterized by optical and scanning electron microscopy and EDS. Results show significant hardening in the subsurface region with little to no formation of secondary phases after tempering.