Heat Treatments and Critical Quenching Rates in Additively Manufactured Al-Si-Mg Alloys

Area of Science:

• Materials Science
• Metallurgy
• Additive Manufacturing

Background:

• Laser powder-bed fusion (LPBF) is a key metal additive manufacturing technique.
• LPBF processing of Al-Si-Mg alloys yields fine microstructures and supersaturated solid solutions.
• Inherent heat treatment during LPBF promotes beneficial alloying element clustering.

Purpose of the Study:

• To investigate the effectiveness of direct aging as a post-heat treatment for LPBF Al-Si-Mg alloys.
• To compare the precipitation hardening behavior of LPBF Al-Si-Mg with cast counterparts.
• To understand the influence of quenching rates on the mechanical properties of LPBF Al-Si-Mg.

Main Methods:

• Laser powder-bed fusion (LPBF) of Al-Si-Mg alloys.
• Direct aging heat treatment applied to as-built samples.
• Microstructural analysis and hardness testing.
• Comparison with cast Al-Si-Mg reference samples.

Main Results:

• Direct aging of LPBF Al-Si-Mg samples did not surpass the hardness of as-built samples.
• LPBF Al-Si-Mg exhibited a significantly higher sensitivity to quenching rates compared to cast samples.
• Achieving similar hardness required 2-3x higher quenching rates for LPBF samples after solution annealing.

Conclusions:

• The fine microstructure and short diffusion paths in LPBF Al-Si-Mg alloys complicate achieving the necessary metastable supersaturation for effective precipitation hardening.
• Higher quenching rates are critical for successful post-heat treatment of LPBF Al-Si-Mg alloys.
• Challenges in achieving optimal precipitation hardening may be more pronounced in larger LPBF components.