Mechanical properties of as-built A356 aluminium alloy processed by Selective Laser Melting

A356 aluminium alloy (AlSi7Mg0.3) is widely used for gravity casting. Its good ductility, strength and corrosion resistance properties make it a compelling material for components requiring high reliability. Examples of parts traditionally built using A356 include engine parts, hydraulic components, brackets, housing covers in automotive, aerospace, and machinery industries [1, 2].
In this post we present the superior mechanical properties of A356 components showing 99.8% relative density [3] and built on the EOSINT M280.

Relative density of finished product

The A356.0 (AlSi7Mg0.3) SLM specimens built using optimum laser irradiation showed 99.8% relative density, measured by the Archimedes method.

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Microstructure
 
Fine dendritic cell microstructures of sub-micron size (approx. 0.5μm) are observed in the horizontal cross section and elongated cell microstructures along the building direction. They seem aligned with the heat flow. These fine cell microstructures are conventionally found in metal components processed by SLM. They are caused by the rapid melting and resolidification of the material [4-7].

[3]

As-built mechanical properties

The dense SLM samples exhibit ultimate tensile strength of 400 MPa, yield strength of 200Mpa and breaking elongation values varying between 12% and 17% depending on the build orientation. These values considerably exceed those typically found for cast melting alloys. The superior mechanical properties of the SLM specimens is usually attributed to the high density combined with fine dendritic cell microstructures.

[3]

Customisation of mechanical properties using post heat treatment

The behaviors of samples manufactured using SLM and the casting is different after heat treatment.  After T5 annealing, E% of SLM samples doubled from 15% in the as-built condition up to 30% in the annealed conditions (350 °C). The ultimate tensile strength decreased from 400MPa to 200MPa. The yield strength decreased from to 250MPa to 125MPa, This may be caused by coarsening of the microstructure.

This implies that the mechanical properties of the SLM components could be tailored to suit various applications.

References
[1] Pio LY. Effect of T6 Heat Treatment on the Mechanical Properties of Gravity Die Cast A356 Aluminium Alloy. J Appl Sci 2011; 11: 2048-52.
[2] Akhter R, Ivanchev L, Burger HP. Effect of pre/post T6 heat treatment on the mechanical properties of laser welded SSM cast A356 aluminium alloy. Mater Sci Eng A 2007; 447: 192-6.
[3] Takahiro Kimura, Takayuki Nakamoto, Microstructures and mechanical properties of A356 (AlSi7Mg0.3) aluminum alloy fabricated by selective laser melting, (2015), doi: 10.1016/j.matdes.2015.10.065
[4] Takaichi A, Suyalatu, Nakamoto T, Joko N, Nomura N, Tatsumi Y, Migita S, Doi H, Kurosu S, Chiba A, Wakabayashi N, Igarashi Y, Hanawa T. Microstructures and mechanical properties of Co-29Cr-6Mo alloy fabricated by selective laser melting process for dental applications. J Mech Behav Biomed Mater 2013; 21: 67-76
[5] Kimura T, Nakamoto T. Microstructures and Mechanical Properties of Al-10%Si-0.4%Mg Fabricated by Selective Laser Melting. J Jpn Soc Powder Powder Metallurgy 2014; 61: 531-7.
[6] Thijs L, Kempen K, Kruth JP, Humbeeck JV. Fine-structured aluminum products with controllable texture by selective laser melting of pre-alloyed AlSi10Mg powder. Acta Mater 2013; 61: 1809-19.
[7] Amato KN, Gaytan SM, Murr LE, Martinez E, Shindo PW, Hernandez J, Collins S, Medina F. Microstructures and mechanical behavior of Inconel 718 fabricated by selective laser melting. Acta Mater 2012; 60: 2229-39.