Al–Mn–Cr–Zr-based alloys tailored for powder bed fusion-laser beam process: Alloy design, printability, resulting microstructure and alloy properties

Abstract

This study introduces a family of unique Al–Mn–Cr–Zr-based aluminium alloys illustrated by two ternary and one quaternary variants. The choice of alloy compositions has created a system resistant to solidification cracking while retaining high amount of solutes in solid solution in as-printed condition. Good relative density (~ 99.5%) has been demonstrated along with microstructural study supported by X-ray diffraction to display solidification structure with nanometric precipitate formation in small amounts in as-printed condition. High levels of Mn and Cr produce significant solid solution strengthening reaching hardness of up to 102 HV in as-printed condition. Additionally, the combination of Mn, Cr and Zr is shown to be important to control precipitation strengthening upon direct ageing and coarsening resistance due to slow diffusivity. To elucidate the concept of precipitation strengthening, one set of alloys was aged at 678 K between 0 and 10 h and microhardness results showed that average hardness response reached 130 HV for the quarternary alloy. Graphical abstract

The Influence of Processing Parameters on the Al-Mn Enriched Nanoprecipitates Formation in a Novel Al-Mn-Cr-Zr Alloy Tailored for Power Bed Fusion-Laser Beam Process

“…The trends revealed three main peaks: the most pronounced at 1.15 AR correlating with nearly spherical particles, a minor peak at 1.7 AR denoting more elongated precipitates and a less pronounced peak at about 2 AR indicating very elongated particles (Figure 9). The results corroborate the optical analysis and align with the observations of Mehta et al [21]. The precipitates size distribution, reported in Figure 10, showed similar trends for the 125 and 150 W processed samples, but separate considerations are needed for the lowest and highest power samples.…”

Microstructure, mechanical properties and fracture mechanisms in a 7017 aluminium alloy tailored for powder bed fusion – laser beam

“…Since the initial amount of added Zr particles was 3 wt% (approx. 1.2 vol%), one can deduce that part of them have molten and dissolved into the matrix (shown previously up to 0.6-0.7 wt% Zr [9,10]). However, since many particles are left (Fig.…”

“…The samples were cut along two directions (parallel and perpendicular to the build direction) followed by mounting on Polyfast conductive resin (from Struers). This was followed by grinding and polishing with 200, 500, 800, 2000 and 4000 grit silica foils followed by polishing with 1 lm diamond-based polish [10].…”

“…This helps to provide sites for heterogeneous nucleation thus reducing stresses at grain boundaries and providing crack free aluminium alloys with isotropic properties. A second method utilized by alloy designers is to develop entirely new alloy recipes [10,11] which provide alloy systems inherently resistant to solidification cracking. Most of the alloy designers have focused on high strength as the most relevant property [6,12,13].…”

“…For example, Cann et al [14] have suggested that the improvement of the load bearing capacity of aluminium above operating temperatures of 493 K could be significantly beneficial for electrical cables and brazed heat-exchangers or heat-sinks. Following this idea, some researchers [9,10,15] have applied the principle of utilizing transitionseries elements such as Mn, Ce or Zr as alloying elements combined with higher solubility enabled via PBF-LB. These studies have shown that thanks to the formation of precipitates at higher temperatures, such systems are resistant to strength loss up to 573 K or higher.…”