High Performance Aluminium Alloys for Laser Powder Bed Fusion: Alloy Design and Development
Licentiate thesis, 2021
This research work focuses on addressing these limitations by working within aluminium alloy systems. It was seen that the prominence of printability issues such as solidification cracking becomes a major hinderance to developing fully dense materials. Alloys processed using LB-PBF were more susceptible to these issues due to the processing conditions, even though the same conditions could make them more desirable in some cases. Thus, simple ways to screen the alloy systems before printing could be used as a quick method to save time. Additionally, the major benefit of LB-PBF comes from rapid solidification wherein solidification rates of few orders of magnitude higher than cast/ wrought alloys are achieved. This can be leveraged to develop new families of Al-alloys, by utilising higher supersaturation of the transition series elements. A few examples are Manganese (Mn), Chromium (Cr) and Zirconium (Zr), which are shown to successfully create printable alloys with solubilities beyond equilibrium.
Printability and high solubility in solid solution of the alloys present a partial solution to the problem. The objective of this study was to showcase high performance Al-alloys, in this case high temperature performance. Mn, Cr and Zr were thus chosen due to their slow bulk diffusivities in aluminium. This means that the nucleation and growth kinetics of the precipitates generated by these elements could be slower than precipitates rich in elements such as Mg and Si. Such an occurrence is lucrative while developing precipitation hardened alloys as the optimum conditions for peak hardness can be controlled relatively easily and improved mechanical properties at high temperature could be expected. Interestingly, it was observed that Al-Mn family of precipitates preferentially grow at grain boundaries in the beginning of heat treatments and later shift to bulk growth. The growth of Al3Zr precipitates, which occurs in the bulk, could be controlled by optimising the kinetics of growth of these Al-Mn family of precipitates. This phenomenon has experimentally shown to provide a secondary hardening in the alloys and reach hardness values corresponding to that of high strength Al-alloys. This phenomenon is novel for Al-alloys as it would be difficult to recreate the same conditions via other processing routes due to significantly lower solubility of transition elements.
Integrated Computational Materials Engineering
Laser Based Powder Bed Fusion
Chalmers, Industrial and Materials Science, Materials and manufacture
B. Mehta, L. Nyborg, K. Frisk, E. Hryha; "Novel Al-Mn based alloys for laser powder bed fusion: alloy design, printability, and microstructure"
B. Mehta, L. Nyborg, K. Frisk; "Precipitation kinetics and microstructural properties of novel Al-Mn-Cr-Zr based alloys developed for laser powder bed fusion"
B. Mehta, A. Svanberg, L. Nyborg; "Laser-powder bed fusion of an Al-Mg-Sc-Zr alloy: Manufacturing, Mechanical and High Temperature Properties"
Lighter components through additive manufacturing of aluminum alloys
VINNOVA (2018-02844), 2018-10-15 -- 2021-10-31.
Manufacturing, Surface and Joining Technology
Metallurgy and Metallic Materials
Areas of Advance
Virtual Development Laboratory, Chalmers Tvärgata 4C, 41258 Göteborg
Opponent: Anders Jarfors, Jönköping University