Element Additives and Fast-Dissolving Agents for Aluminum Alloy Production

In aluminum alloy production, aluminum-based master alloys are commonly used for batching and composition adjustment. This method can accurately control the chemical composition of finished aluminum alloy products. However, because most master alloys contain relatively low amounts of alloying elements, the required addition amount is often large. To reduce the amount of master alloy added and lower production costs, element additives have been developed and widely used.

What Are Element Additives?

Element additives are non-sintered powder metallurgy products. They are usually made by mechanically mixing pure metal powder of suitable particle size with sodium-free flux powder, and then pressing the mixture into cake-shaped blocks.

At present, commercial element additives are generally composed of three parts:

1. Alloying element powder
2. Aluminum powder
3. Flux powder

According to the YS/T 492-2005 standard for aluminum and aluminum alloy composition additives, the commonly specified additives include iron additive, manganese additive, copper additive, chromium additive, and titanium additive. The pure metal content is generally 75% ± 3%. Other grades, specifications, and chemical compositions may be agreed upon by both supplier and buyer in the contract.

Common Element Additives and Their Uses

Element additives are mainly used to adjust the content of alloying elements in aluminum alloys. Typical products include:

• Iron additive: used to adjust Fe content in aluminum alloys.
• Manganese additive: used to adjust Mn content.
• Copper additive: used to adjust Cu content.
• Chromium additive: used to adjust Cr content.
• Silicon additive: used to adjust Si content.
• Zirconium additive: used to adjust Zr content.
• Titanium additive: used to adjust Ti content.

Most element additives are used at around 750 ± 5°C. The common block weight is about 500 ± 5g. Since the additives contain a certain amount of flux, they can absorb moisture, so moisture control is very important.

Storage and Packaging Requirements

Element additives should be packed in plastic bags. Each bag generally contains 4 to 5 blocks, and each carton contains 6 to 10 bags.

According to the YS/T 492-2005 standard, the packaging bag color should be distinguished by additive type:

• Iron additive: green
• Manganese additive: purple-red
• Chromium additive: blue
• Copper additive: yellow
• Titanium additive: red

Element additives should be stored in a ventilated and dry warehouse. During storage, deliquescence or moisture absorption should not occur. The storage period should not exceed 6 months. Products stored for more than 6 months can still be used after passing inspection.

Main Characteristics of Element Additives

Element additives have several important advantages in aluminum alloy production.

First, the alloying element content is higher than that of ordinary master alloys. This reduces the required addition amount and lowers transportation, storage, and management costs.

Second, alloying elements are added in powder form. The particle size is usually 50 to 200 μm, giving a large specific surface area. As a result, the additive amount is small, the temperature drop after addition is limited, the melting speed is fast, and both time and energy can be saved.

Third, element additives have relatively high density. The density of iron, manganese, copper, and chromium additives is generally 3.4 to 4.0 g/cm³, while the density of titanium additive is about 2.9 to 4.0 g/cm³. These additives can easily enter the aluminum melt. With flux protection, they dissolve quickly and provide a relatively high recovery rate.

According to standard requirements, the actual recovery rate of manganese, copper, and chromium additives should not be less than 95%, while the actual recovery rate of iron and titanium additives should not be less than 90%. For example, additives containing 75% chromium, manganese, iron, and copper can reach a 95% recovery rate at 720°C in about 23 minutes, 14 minutes, 9 minutes, and 2.5 minutes respectively.

Fourth, the alloying element content is accurate, and the block weight is stable and small, making batching and composition adjustment more convenient. According to YS/T 492-2005, the diameter of additive cakes is generally 80 to 90 mm, and the thickness is usually 20 to 40 mm.

What Are Fast-Dissolving Agents?

Fast-dissolving agents are new products developed on the basis of ordinary element additives. Their dissolution speed is faster than that of common element additives.

Compared with ordinary element additives, fast-dissolving agents have the following features:

1. Faster dissolution speed, about twice as fast as ordinary element additives.
2. Lower operating temperature, generally 690 to 720°C.
3. Higher recovery rate, usually about 95% for silicon additives and about 98% for iron and manganese additives.
4. No sodium salt or chloride salt, no moisture absorption, and suitable for storage and transportation.

Production Methods of Fast-Dissolving Agents

There are currently two main production methods for fast-dissolving agents.

The first method is to attach a layer of flux that can react with the aluminum melt and release heat onto the surface of metal blocks with suitable particle size. This accelerates metal dissolution. Examples include fast-dissolving crystalline silicon.

The second method is to use fluoride salt instead of chloride salt and mix it with metal powder, aluminum powder, catalyst, flux assistant, and a small amount of aluminum powder. After uniform mixing, the material is pressed into cake-shaped products. When added into aluminum melt, a local high-temperature zone is generated through exothermic reaction, accelerating the dissolution of metal powder. Common examples include fast-dissolving silicon additive, fast-dissolving iron additive, and fast-dissolving manganese additive.

Conclusion

Element additives and fast-dissolving agents are important materials for aluminum alloy composition adjustment. Compared with traditional aluminum-based master alloys, element additives have higher alloying element content, smaller addition amount, faster melting speed, convenient batching, and lower storage and transportation costs.

Fast-dissolving agents further improve dissolution speed and recovery rate, and can be used at lower temperatures. They are especially useful for aluminum alloy production processes that require accurate composition control, lower energy consumption, and higher production efficiency.