A combination strategy for additive manufacturing of AA2024 high-strength aluminium alloys fabricated by laser powder bed fusion: Role of hot isostatic pressing

Abstract

Hot cracks and pores remain major obstacles for the practical application of high-strength aluminium alloys fabricated by laser powder bed fusion (LPBF). A combination manufacturing strategy, integrating functional treatment of feedstock, inoculation treatment and hot isostatic pressing (HIP) post-processing, was used to tackle this issue. Crack-free AA2024 alloys with fine equiaxed grains were manufactured by LPBF via incorporating TiC and TiH2 grain-refining particles. However, when the build rate increases from 0.36 mm3/s to 2.16 mm3/s, the relative density decreases from 97.0% to 93.3%, resulting in a decline in the ultimate tensile strength (UTS) and elongation (El) of as-built samples from 395 ± 20 MPa and 10.2 ± 2.1% to 347 ± 17 MPa and 3.5 ± 1.3%, respectively. By healing pores and controlling precipitates, HIP reduces the properties difference between high-speed and low-speed printed alloys. After HIP treatment, the typical network eutectics that segregated at the grain boundaries evolve into spherical θ-Al2Cu dispersoids without any obvious grain coarsen. T-Al20Cu2Mn3 and Al18Ti2Mg3 intermetallic phases with twin substructure appear in the samples, which is beneficial to dispersion strengthening of alloys. The high-speed printed samples exhibit an excellent UTS of 462 ± 23 MPa and an El of 12.6 ± 2.4%, which is comparable to those of low-speed printed samples. Thus, for critical applications that require high productivity, HIP is a promising post-processing solution to minimise the deterioration of mechanical properties caused by porosity in high-speed printed alloys.