Date of Award

January 2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Meysam Haghshenas

Abstract

Selective Laser Melting (SLM) additive manufacturing of aluminum alloys is a layer-wise manufacturing method which can provide lightweight and complex-in-shape automotive, aerospace and medical components with enhanced mechanical properties. In the SLM, the mechanical properties will differentiate depending on the cooling rate as the deposition of material gradation distance from the build plate as well as the deposition direction, in which it has an effect on the microstructure.

The aim of this project is to assess the correlation between microstructure and small-scale characteristics of an additive manufactured AlSi10Mg alloy in the as-printed and heat treated conditions. Post heat treatment cycle were conducted at the elevated temperature of 520 ℃ solutionizing and then followed by four different cooling rates: water quenching (WQ), air cooling (AC), furnace cooling (FC) and artificial ageing (soaking at 170 ℃ for 4 hours). The post heat treatment is utilized to homogenize the microstructure and dissolve the formation of anisotropy in the microstructure thus improve the ductility and strengthening the alloy.

Along with the microstructural assessments through optical and scanning electron microcopies, small scale characterizations were performed utilizing a nanoindentation testing approach, a non-destructive, robust, and reliable testing technique.

The Findings show a transformation in the microstructure from cellular grains in the as-printed materials, with needle like silicon fiber colonies, to fragmented coarsened eutectic silicon particles upon the heat treatment. Moreover, coarsened and spheroidized silicon particles, with different sizes, were observed upon various heat treatment cycles. Unlike cast AlSi10Mg alloys, upon heat treatment in the SLM AlSi10Mg alloy, the hardness is decreased which is mainly caused by silicon spheroidization phenomena. Whereas due to the fine microstructure resulted from dual impact of rapid melting and directional cooling caused by repeated cycles of heating, the as-print sample exhibited the highest hardness value. In this project, a comparison of the various SLM AlSi10Mg samples was conducted to understand the correlations between the mechanical properties and produced microstructure and to fully understand spheroidization phenomena.

Download

Share

COinS