Laser sintering of blended Al-Si powders
Eyitayo Olatunde Olakanmi
Institute for Materials Research, University of Leeds, Leeds, UK
Kenneth W. Dalgarno
School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne, UK, and
Robert F. Cochrane
Institute for Materials Research, University of Leeds, Leeds, UK
Abstract
Purpose – The purpose of this paper is to study the effects of particle size distribution, component ratio, particle packing arrangement, and chemical
constitution on the laser sintering behaviour of blended hypoeutectic Al-Si powders.
Design/methodology/approach – A range of bimodal and trimodal powder blends were created through mixing Al-12Si and pure aluminium
powder. The powder blends were then processed using selective laser sintering to investigate the effect of alloy composition, powder particle size and
bed density on densification and microstructural evolution.
Findings – For all of the powder blends the sintered density increases with the specific laser energy input until a saturation level is reached. Beyond
this saturation level no further increase in sintered density is obtained for an increase in specific laser energy input. However, the peak density achieved
for a given blend varied significantly with the chemical constitution of the alloy, peaking at approximately 9 wt% Si. The tap density of the raw powder
mixture (assumed to be representative of bed density) was also a significant factor.
Originality/value – This is the first study to consider the usefulness of silicon as an alloying element in aluminium alloys to be processed by selective
laser sintering. In addition the paper outlines the key factors in optimising processing parameters and powder properties in order to attain sound
sinterability for direct laser sintered parts.
Keywords Alloys, Sintering, Particle size measurement, Additive manufacturing, Selective laser sintering, Aluminium alloy,
Hypoeutectic Al-Si powders
Paper type Research paper
1. Introduction
In selective laser sintering (SLS) of metal powders, powder
properties such as particle size and size distribution, component
ratio, nature of particle packing arrangement, and chemical
constitution play key role in the manipulation of its sintering
response (Simchi, 2006; Nakamoto et al., 2009). However,
literature on the effects of particle packing arrangements on the
microstructure of SLS processed components is very scarce,
especially related to aluminium alloy powders. In the case of
steel powders research has generally addressed powder
contamination issues rather than actual particle packing
effects on microstructure (Niu and Chang, 2000; Zhu et al.,
2007). Results from those studies have not been able to
completely define what direct consequences the nature of
particle packing arrangements has on the processing conditions,
densification, and microstructure of laser sintered components.
The research reported in this paper has investigated the role
of powder properties in determining the bed density,
processed part density and microstructure of aluminium
alloys, using blended hypoeutectic Al-12Si powders as the
material for investigation. Silicon is commonly used as an
alloying element for aluminium alloys which will be cast. The
addition of silicon produces an alloy with a lowered melting
temperature (Callister, 2007) and viscosity (Dinsdale and
Quested, 2004), and both of these effects were considered to
be of potential value for SLS, making it easier to generate
molten material, and easier for that molten material to wet
surrounding material.
2. Materials, equipment, and experimental
procedure
2.1 Materials
The starting materials were powders designated as pre-alloyed
Al-12Si, and pure aluminium AL-1, AL-2, AL-3, and AL-4,
having varying particle sizes and distributions as outlined in
Table I. All were produced by inert gas atomisation.
The four different pure Al powders AL-1 (45-75
m
m), AL-2
(10-45
m
m), AL-3 (17-30
m
m), and AL-4 (10-14
m
m) were
blended with Al-12Si at concentrations of 10, 25, 30, 40, and
50 wt%. In addition four trimodal powder mixes containing
75 wt% Al-12Si powder, and proportions of AL-3 and AL-4
varying between 5 and 25 per cent were also prepared.
Details of all of the powder blends are shown in Table II.
The current issue and full text archive of this journal is available at
www.emeraldinsight.com/1355-2546.htm
Rapid Prototyping Journal
18/2 (2012) 109 –119
q Emerald Group Publishing Limited [ISSN 1355-2546]
[DOI 10.1108/13552541211212096]
Eyitayo Olatunde Olakanmi wishes to acknowledge the Commonwealth
Scholarship Commission in the UK for the sponsorship of this study at the
Institute for Materials Research, University of Leeds.
Received: 23 July 2010
Revised: 14 December 2010, 25 February 2011
Accepted: 13 April 2011
109