Hot Isostatic Pressing of Aluminum–Silicon Alloys Fabricated by Laser Powder-Bed Fusion

Abstract

Hot isostatic pressing can be utilized to reduce the anisotropic mechanical properties of Al–Si–Mg alloys fabricated by laser powder-bed fusion (L-PBF). The implementation of post processing densification processes can open up new fields of application by meeting high quality requirements defined by aircraft and automotive industries. A gas pressure of 75 MPa during hot isostatic pressing lowers the critical cooling rate required to achieve a supersaturated solid solution. Direct aging uses this pressure related effect during heat treatment in modern hot isostatic presses, which offer advanced cooling capabilities, thereby avoiding the necessity of a separate solution annealing step for Al–Si–Mg cast alloys. Hot isostatic pressing, followed by rapid quenching, was applied to both sand cast as well as laser powder-bed fused Al–Si–Mg aluminum alloys. It was shown that the critical cooling rate required to achieve a supersaturated solid solution is significantly higher for additively manufactured, age-hardenable aluminum alloys than it is for comparable sand cast material. The application of hot isostatic pressing can be combined with heat treatment, consisting of solution annealing, quenching and direct aging, in order to achieve both a dense material with a small number of preferred locations for the initiation of fatigue cracks and a high material strength.

Additive Manufacturing of AlSi10Mg and Ti6Al4V Lightweight Alloys via Laser Powder Bed Fusion: A Review of Heat Treatments Effects

“…In this scenario, Ertuğrul et al [ 107 ] also combined the HIP HT with the T6 to increase the mechanical properties, but the round Si particles become larger and more spherical, and the microstructure shows needle-like Fe-rich phases. The same results were reported by Schneller et al [ 108 ] and Hafenstein et al [ 167 ] who showed a decrease between 64 and 66% of the internal pores.…”

“…In conclusion, the HIP HT, which can be used to reduce the internal pores inducing the sample’s densification, confers the same microstructural effects of the T6 HTs [ 107 , 108 , 167 ]. Merino et al [ 165 ] showed a complete recrystallization process after HIP (515 °C × 3 h × 100 MPa) and HIP + T6 (515 °C × 3 h × 100 MPa) + ((530 °C × 6 h) + (160 °C × 6 h)) HTs.…”

Understanding the role of additive manufacturing in the development of astronomical hardware

“…An error during the HIP meant that the target temperature (500 • C) was exceeded and a constant temperature of ∼570 • C was recorded over the 4 hrs of the HIP heating phase. This temperature is higher than commonly used for L-PBF aluminium 31 (510 • C to 540 • C) and, as such, the effect the aluminium micro-structure is unclear. Therefore, the role of HIP on surface roughness after SPDT requires further investigation.…”

Ongoing Challenges of Laser-Based Powder Bed Fusion Processing of Al Alloys and Potential Solutions from the Literature—A Review

“…Although this kind of porosity is commonly not considered detrimental to mechanical performance thanks to their small size and spherical shape, extreme applications, such as in the aerospace field, need to achieve a perfect densification of the component. To achieve this goal, tailored post-processing operations, such as hot isostatic pressing (HIP), need to be defined [ 87 ].…”