Aluminum alloy cooling rates

Unlock Stronger Aluminum: The Secret of Cooling Rates in Alloy Production

Avery Sinclair in Tech & Innovation December 2025 • 4 min read.

"Discover how controlling cooling during the production of Al-3%B-3%Sr master alloys can dramatically improve the grain refinement and modify the efficiency of A356 aluminum alloys."

Aluminum-silicon-magnesium (Al-Si-Mg) and aluminum-silicon-copper (Al-Si-Cu) based alloys are go-to choices for complex cast parts. Their excellent castability and resistance to hot tearing make them ideal. To boost their strength, engineers use precipitation strengthening by carefully managing the size of precipitated particles like Mg2Si or Al₂Cu.

In the world of aluminum casting, melt treatment is key. This involves either refining the grain structure with additives like Al-Ti or Al-B master alloys or modifying the eutectic phase using Al-Sr alloys. Grain refinement creates finer alpha-aluminum (α-Al) grains by providing more nucleation sites during solidification. Eutectic modification enhances mechanical properties and improves how the molten alloy fills molds, ultimately reducing porosity and the need for extensive heat treatments.

The combination of grain refiners and modifiers can lead to superior mechanical properties. Recent developments have introduced Al-Ti-B-Sr and Al-B-Sr master alloys, which create particles like TiB2, TiAl3, AlB2, and SrB6. These act as heterogeneous nucleation sites, promoting grain refinement and modifying the alloy's structure simultaneously.

The Cooling Rate Effect: How It Changes Alloy Structure

Researchers investigated how different cooling rates affect the size and shape of particles in Al-3%B-3%Sr master alloys. They produced two alloys, one slowly cooled at 0.2°C/s (M1) and another rapidly cooled at 10°C/s (M2). These alloys were then tested for their ability to refine grain structure and modify the eutectic silicon in A356 alloys. A 4wt% addition was used, with holding times ranging from 10 to 120 minutes.

The study revealed significant differences in the microstructure of the two alloys:

M1 Alloy (Slow Cooling): Showed larger, solidified particles of AlB2, SrB6, and Al4Sr within the α-Al matrix.
M2 Alloy (Rapid Cooling): Displayed smaller particles of the same compounds.

When added to A356 alloy, the M1 alloy resulted in smaller grain sizes and fully modified eutectic silicon, particularly with holding times between 10 and 60 minutes. The M2 alloy achieved small grain sizes more quickly (10-30 minutes), but the eutectic silicon was only partially modified. Thermal analysis confirmed that adding the Al-3%B-3%Sr master alloy changed the solidification process of the A356 alloy, reducing undercooling during nucleation and the eutectic reaction, and extending the overall solidification time.

Key Takeaways: Optimizing Aluminum Alloy Production

This research highlights the crucial role of cooling rates in producing Al-3%B-3%Sr master alloys. Slow cooling leads to larger particles, which can be more effective in refining grain structure and modifying eutectic silicon in A356 alloys.

The size and morphology of AlB2 and SrB6 particles directly impact the alloy's performance. While rapid cooling creates smaller particles, they may not be as effective in achieving the desired modifications.

By carefully controlling the cooling rate during master alloy production, manufacturers can fine-tune the properties of their aluminum castings, leading to stronger, more durable, and higher-performing components.

About this Article -

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This article is based on research published under:

DOI-LINK: 10.1051/matecconf/201819201036, Alternate LINK

Title: Effect Of Cooling Rates Of Production Process Of Al-3%B-3%Sr Master Alloy On Grain Refinement And Eutectic Modification Efficiency In Cast A356 Alloy

Subject: General Medicine

Journal: MATEC Web of Conferences

Publisher: EDP Sciences

Authors: Krittee Eidhed, Phisith Muangnoy

Published: 2018-01-01

Everything You Need To Know

How does the cooling rate impact the properties of aluminum alloys made with Al-3%B-3%Sr master alloys?

The cooling rate during the production of Al-3%B-3%Sr master alloys significantly impacts the resulting aluminum alloy's strength and structure. Slower cooling rates, such as 0.2°C/s as seen in alloy M1, result in larger particles of AlB2, SrB6, and Al4Sr within the α-Al matrix. These larger particles are more effective at refining the grain structure and modifying eutectic silicon in A356 alloys, leading to enhanced mechanical properties. In contrast, faster cooling rates, like 10°C/s in alloy M2, produce smaller particles that may not fully modify the eutectic silicon.

What role do grain refiners and modifiers play in enhancing the properties of aluminum castings?

Grain refinement in aluminum casting uses additives such as Al-Ti or Al-B master alloys to create finer alpha-aluminum (α-Al) grains. This is achieved by providing more nucleation sites during solidification, which leads to a more uniform and stronger material. Eutectic modification, often done using Al-Sr alloys, improves the alloy's mechanical properties and mold-filling capabilities, reducing porosity and the need for extensive heat treatments. When combined, grain refiners and modifiers containing particles like TiB2, TiAl3, AlB2, and SrB6 in master alloys such as Al-Ti-B-Sr and Al-B-Sr enhance both grain refinement and eutectic structure simultaneously.

Why are aluminum-silicon-magnesium (Al-Si-Mg) and aluminum-silicon-copper (Al-Si-Cu) alloys preferred for complex cast parts, and how is their strength improved?

Alloys like Al-Si-Mg and Al-Si-Cu are frequently chosen for creating intricate cast parts due to their excellent castability and resistance to hot tearing. To increase the strength of these alloys, precipitation strengthening is employed. This process involves carefully controlling the size of precipitated particles such as Mg2Si or Al₂Cu. Optimizing the size and distribution of these particles enhances the alloy's mechanical properties, providing the required durability and performance for complex applications.

In the study, what differences were observed between the slowly cooled (M1) and rapidly cooled (M2) Al-3%B-3%Sr master alloys, and how did these differences affect their ability to refine A356 aluminum?

Researchers found that different cooling rates significantly affect the microstructure and performance of Al-3%B-3%Sr master alloys in refining A356 aluminum. The M1 alloy, cooled slowly at 0.2°C/s, had larger particles of AlB2, SrB6, and Al4Sr and was most effective between 10 and 60 minutes of holding time. The M2 alloy, cooled rapidly at 10°C/s, had smaller particles and achieved faster grain size reduction (10-30 minutes), but it only partially modified the eutectic silicon. Therefore, slow cooling rates during the production of Al-3%B-3%Sr master alloys prove more effective in refining A356 alloys.

How does adding Al-3%B-3%Sr master alloys influence the solidification process of A356 alloys, and what further research could enhance our understanding?

The addition of Al-3%B-3%Sr master alloys to A356 alloys alters the solidification process by reducing undercooling during nucleation and the eutectic reaction, and by extending the overall solidification time. This impacts the final microstructure and mechanical properties of the A356 alloy. Further studies could explore how varying the percentage composition of B and Sr in the Al-B-Sr master alloy and the addition of other elements can optimize the alloy's performance under different thermal conditions and mechanical stresses.