Alloying Additives for Aluminium Alloys

Topics Covered

Background

Alloying Additive

Flux for Speedy Dissolution

Key Features

Recommended Addition Practice

Background

Alloying tablets are used in casthouses world-wide for the manufacture of high-quality aluminium alloys in applications such as rolling ingot for foilstock and canstock, billet for precision extrusions and high-quality foundry casting alloys. For the precise compositional adjustment of alloy melts or for bulk element addition, it is the optimum choice.

Alloying tablet popularity has grown steadily since its introduction in the early 1980s. These concentrated additives are a carefully controlled mixture of alloying element (75%, 80%, 85% and in some cases up to 100%) in powder, sponge or needle form, aluminium powder and optional sodium-free non-hygroscopic flux. Dissolution relies on the alloying element powder particles forming aluminides. Stirring the melt greatly enhances dispersion of the aluminides, resulting in improved recoveries.

Flux for Speedy Dissolution

Some grades of alloying tablets contain flux – preferred where speed of dissolution is important or when low melt temperatures and stirring difficulty are issues. The flux aids in removal of the oxide film found on any powder, sponge or needle particle to expose the metallic element to molten aluminium, promoting rapid dissolution.

Key Features

•        Rapid dissolution at normal casthouse operating temperatures.

•        Concentrated form means reduced inventory, transport and storage costs compared with binary master alloys.

•        High element recovery – typically over 95%.

•        Minimal temperature loss upon addition.

•        Accurate and clean addition with no weighing needed for packaged product.

•        Rapid, consistent solubility of self-sinking tablets means less energy and less cost.

•        Precise weight and easy handling with color-coded, light-weight packs.

Recommended Addition Practice of Alloying Tablets

After calculating the required addition, skim off heavy dross and add the self-sinking alloying packs, or individual tablets evenly over the melt surface. Hold the bath temperature for 5-10 minutes, with a recommended minimum temperature of 720°C (1,328°F), then stir well to maximize recovery and homogeneity. These smaller tablets were developed for applications such as additions to channel induction furnaces, transfer launders, semi-automatic bulk charging systems and precise compositional adjustment for smaller foundries. The versatile briquetted compacts also allow accurate addition and adjustment in many applications.

Original material sourced from Metallurg Aluminium