Date of Award

12-14-2015

Document Type

Open Access Thesis

Department

Mechanical Engineering

First Advisor

Anthony Reynolds

Abstract

The purpose of this study is to investigate the friction stir welding (FSW) tool material degradation factors due variation in tool material properties and the effect of an aluminum diffusion wear mechanism on three different FSW tool material when exposed to various welding temperatures and times. The degradation factors are essential to FSW tool design due to the effect of the tool pin and shoulders on the heat generation and material flow which directly correlated to the weld quality created during the FSW process. For this investigation the three materials used are H13, TSP1, and MP159. To determine degradation factors the variations in microstructure, hardness, nominal impact energy, fracture surface of impacted specimens, surface roughness of impacted specimens, and the effect of aluminum diffusion on each of the materials is analyzed. The hardness test revealed that in the range of welding temperature and time exposure testing there is a hardness variation of 550-460 HV for H13, 550 - 526 HV for MP159, and 813-704 HV for TSP1. The Izod testing concluded that MP159 requires the highest nominal impact energy to cause failure, correlating to the highest surface roughness, while TSP1 requires the lowest nominal impact energy to cause failure, which correlates to the lowest surface roughness. Based off of the fractography results all of the materials failed due to microvoid coalescence and this is proof of a ductile failure mechanism. Lastly, the aluminum diffusion experiments did show evidence an aluminum diffusion surface reaction in TSP1 and MP159 along with mechanical mix layers in each of the materials however, there is no proof of aluminum penetration along the tool materials’ grain boundaries.

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