Abstract
The aim of this work is to investigate the influence of the addition of Cu on the microstructure and on the microhardness of a laser powder bed fusion (L-PBF)-fabricated AlSi10MgCu alloy. With this goal, AlSi10Mg+4 wt%Cu pre-alloyed powder was produced by gas atomization. Following a parameter optimization study, dense as-built specimens with a high relative density of 99.8% were fabricated. An outstanding microhardness value, exceeding 180 HV, was obtained after aging at 160 °C for 16 h. This value is similar to that of the high strength Al 7075 in the T6 condition. With the aid of analytical transmission electron microscopy, it was concluded that the origin of the observed excellent mechanical behavior could be attributed to the beneficial effect of Cu in reducing the Al-matrix cell size, and in increasing the density and decreasing the size of the Si-based nanoprecipitates at cell interiors. More specifically, it is proposed that the maximum hardness is associated to the development of Cu-rich GP-I zones, which act as precursors of Si nanoprecipitates. Overaging leads to a reduction in microhardness due to transformation of these GP-I zones into coarser θ’’ precipitates and thus to a smaller volume fraction of larger Si-based nanoparticles.
Highlights
Laser powder bed fusion (L-PBF) is an emerging Additive Manufacturing (AM) technique by which successive powder layers are consolidated to make complex geometry parts in a near-net-shape manner [1]
The morphology, size, and microstructure of the atomized powder were carefully characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Figs. 1 and 2)
The high angle annular dark field (HAADF)-STEM micrograph, and the corresponding elemental map, shown in Fig. 2b and c, respectively, reveal that the intercellular regions are populated by Si- and Cu-based particles that grow adjacent to each other
Summary
Laser powder bed fusion (L-PBF) is an emerging Additive Manufacturing (AM) technique by which successive powder layers are consolidated to make complex geometry parts in a near-net-shape manner [1]. Besides allowing to fabricate components with intricate geometry, L-PBF constitutes a tool to design and process novel advanced materials, since the high cooling rates involved (104–107 K/s), which are much faster than the rates associated to conventional pro cessing methods (~102 K/s), may give rise to notable changes in the solidified microstructure, including grain refinement, precipitation of out-of-equilibrium phases, increased solid solubility and reduced segregation [2]. The number of metallic powder feedstock alloys that can be utilized to build defect-free components with high performance is still very limited. The physical properties of Al alloys, including a high tendency to oxidation, high thermal conductivity, and large solidifica tion shrinkage, as well as the low flowability and high laser reflectivity of Al powders, are pointed as major hindrances to AM production of these materials [4,5]
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