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

Stephan Hafenstein,Andreas Öchsner,Enes Sert,Ewald Werner,Leonhard Hitzler,Markus Merkel

doi:10.3390/technologies8030048

Stephan Hafenstein, Andreas Öchsner + Show 4 more

Open Access

https://doi.org/10.3390/technologies8030048

Copy DOI

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.

Highlights

Hot isostatic pressing of Al–Si–Mg cast material is conventionally performed at a pressure of75 MPa, a temperature of 510 ◦ C and for a duration of 120 min
The quasistatic mechanical properties of the sand cast aluminum alloy AlSi7Mg0.3 were improved by the application of hot isostatic pressing followed by quenching at 1 K/s
The same hot isostatic pressing resulted in a higher material strength, if thewere samples were subsequently isostatic pressing resulted in a higher material strength, if the samples subsequently artificially artificially aged(Series

Summary

Introduction

Hot isostatic pressing of Al–Si–Mg cast material is conventionally performed at a pressure of. Particularity, the high cooling rates during the L-PBF result in a supersaturated solid solution of alloying elements, enabling to achieve high material strength via the precipitation of intermetallic phases during aging [4,5,6]. Conventional hot isostatic pressing of age hardenable Al–Si–Mg alloys is known to remove casting porosity entirely and is performed at a pressure of 75 MPa, at a temperature of 510 ◦ C and for a duration of 120 min. A pressure induced decease in the critical cooling rate allows direct aging of cast Al–Si–Mg alloys, if the cooling rate after hot isostatic pressing is high enough to avoid the precipitation of alloying elements during cooling [21,26,27,28]. Hot isostatic pressing can be utilized to reduce the porosity of different L-PBF materials [34,35,36]

Experimental

HIP Process and Heat Treatment

Results and Discussion

Summary and Outlook