Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion.

Matteo Vanzetti,Enrico Virgillito,Federica Bondioli,Mariangela Lombardi,Diego Manfredi,Alberta Aversa,Paolo Fino

doi:10.3390/ma14206157

Abstract

Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 °C followed by water quenching and subsequently by an artificial aging at 170 °C for 2–8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 °C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 °C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry.

Highlights

Laser powder bed fusion (L-PBF) can be used to process a wide variety of metallic materials such as steel, titanium, nickel, and aluminum alloys
Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures
The results show that a 15 min solution treatment at 540 ◦C allows the dissolution of the very fine phases obtained during the laser powder bed fusion (L-PBF) process; the subsequent heat treatment at 170 ◦C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6

Summary

Introduction

Laser powder bed fusion (L-PBF) can be used to process a wide variety of metallic materials such as steel, titanium, nickel, and aluminum alloys. High residual stresses and the fine microstructural features lead to low elongation at failure values [9] Based on these considerations, it is clear that the heat treatments for AlSi7Mg alloys processed by L-PBF still need to be studied and optimized. The purpose of this work is to evaluate the effects of a short heat treatment L-PBF AlSi7Mg samples, characterized by a solution heat treatment of 15 min followed by water quenching and subsequently by an artificial aging at 170 ◦C for 2–8 h With this aim, the mechanical properties and the microstructure of the obtained samples were studied in comparison with as-built and direct-aged conditions

Materials and Methods

Hardness

Findings

Microstructure