Cyclic deformation behavior of an automotive material

Amir Reza Emami, Ryerson University

Date of Award

2008

Degree Type

Thesis Project

Degree Name

Master of Engineering (MEng)

Department

Mechanical Engineering

First Advisor

Daolun Chen

Abstract

The A356 Al-Si-Mg cast alloy is being used in the automotive industry to replace some heavy components due to its fabrication flexibility and high strength-to-weight ratio. This study was aimed at identifying cyclic deformation characteristics and fracture mechanisms of the A356 alloy in different material conditions. The microstructure consisted of primary a-Al matrix and eutectic regions containing Si particles of acicular (T5) and spherical (T6 and ModT6) morphologies. The ModT6 sample had a higher yield strength (YS) and ultimate tensile strength (UTS) but a lower strain hardening exponent than the T6 sample, while the T5 sample had a lower YS UTS but a higher initial strain hardening than the T6 sample.

The T6 sample exhibited a higher cyclic hardening capacity and longer fatigue life. Crack initiation in both tensile and fatigue tests occurred at the sub-surface voids. Quasi-cleavage fracture characteristics in the T5 condition and dimple-like fracture features in the T6 and ModT6 were observed.