Selective laser melting of hypereutectic Al-Si40-powder using ultra-short laser pulses

T Ullsperger,G Matthäus,A Tünnermann,S Nolte,S Risse,H Engelhardt,L Kaden,M Rettenmayr

doi:10.1007/s00339-017-1337-z

Abstract

We investigate the use of ultra-short laser pulses for the selective melting of Al-Si40-powder to fabricate complex light-weight structures with wall sizes below 100,upmu text {m} combined with higher tensile strength and lower thermal expansion coefficient in comparison to standard Al–Si alloys. During the cooling process using conventional techniques, large primary silicon particles are formed which impairs the mechanical and thermal properties. We demonstrate that these limitations can be overcome using ultra-short laser pulses enabling the rapid heating and cooling in a non-thermal equilibrium process. We analyze the morphology characteristics and micro-structures of single tracks and thin-walled structures depending on pulse energy, repetition rate and scanning velocity utilizing pulses with a duration of 500,text {fs} at a wavelength of 1030,text {nm}. The possibility to specifically change and optimize the microstructure is shown.

Highlights

Selective laser melting and sintering (SLM/SLS) of metal powders evolved as one of the most promising tools for the fabrication of three-dimensional freeform elements with highly sophisticated geometries that cannot be processed with conventional machining methods or casting techniques [1, 2]
The eutectic point of this binary system is located at a mass fraction of 12.2% silicon and 577 ◦C [6, 7]
The smallest sizes that could be achieved with hypereutectic Al–Si powders are above 150 μm using laser cladding with a cw laser [14, 15]

Summary

Introduction

Selective laser melting and sintering (SLM/SLS) of metal powders evolved as one of the most promising tools for the fabrication of three-dimensional freeform elements with highly sophisticated geometries that cannot be processed with conventional machining methods or casting techniques [1, 2]. One outstanding advantage is a high level of flexibility in the design of tailored and optimized light-weight structures In this context, aluminium as a major alloy component is predominantly used due to the combination of low density, high thermal conductivity and low material costs. Up to now only a few methods such as spray deposition and melt spinning allow a rapid cooling that is suitable to achieve a desired fine distribution of silicon particles in an aluminium matrix [9,10,11,12]. These techniques only allow the fabrication of semi-finished products without complex designed structures. The smallest sizes that could be achieved with hypereutectic Al–Si powders are above 150 μm using laser cladding with a cw laser [14, 15]

Methods

Results

Conclusion