Use of KBF₄–Al mixed powder to produce boron-bearing 6063 aluminum alloys

Abstract

In this study, a simple B addition process for producing 6063 aluminum alloy containing 0.03% B was investigated. KBF₄ (98.0 mass%) and commercial-purity aluminum powder (>99.7 mass%, particle size: 30 µm) were weighed, mixed, wrapped in aluminum foil, and placed in a phosphorizer. The phosphorizer was then immersed in a molten 6063 aluminum alloy at a temperature of 720, 760, 810, or 860°C. The boron recovery rate depends on the amount of aluminum powder in the mixture and the melt temperature. Optimizing these factors gives a 90% boron recovery rate. Excess aluminum powder in the mixture leads to an increase in the specific surface area of the KBF₄ particles and promotes the reaction, 2KBF₄+3Al→AlB₂+2KAlF₄. The AlB₂ contained within the KAlF₄ migrates into the melt as the KAlF₄ evaporates. Therefore, a mixed powder of KBF₄ and Al can be an effective means of adding boron to 6063 aluminum alloy if the amount of aluminum and the temperature are carefully controlled. For the present experimental conditions, it was difficult to find AlB₂ in the alloy by EPMA, because only a small amount of B was added. B seems to form a solid solution with aluminum without forming coarse intermetallic compounds.