Abstract No.:	7034
Scheduled at:	Wednesday, May 05, 2021, Hall 1 10:30 AM Materials
Title:	AMAG TopClad®PURE for improved brazeability
Authors:	Gerhard Hanko / AMAG rolling GmbH, Austria Alexander Trier / AMAG rolling GmbH, Austria Petra Morak*/ AMAG rolling GmbH, Austria Stefan Hainthaler/ AMAG rolling GmbH, Austria Michael Hemetsberger/ AMAG rolling GmbH, Austria
Abstract:	Flat rolled brazing sheet is covered with a stable, oxidic coating, which must be either removed or broken up before brazing. Vacuum Brazing (VB) requires enough Magnesium in the filler and Controlled Atmosphere Brazing (CAB) uses flux which dissolves the oxide layer in the molten state to enable material flow. Generally, it can be stated a thinner oxide layer means a more robust brazing process to achieve satisfying brazing results. In addition to the natural oxide skin, hot rolled coils are also covered by an ultra-thin layer of roll coating impurities, because hot rolling of Aluminium inherently involves a constant transfer of metal and oxidic compounds between the surface of the roll and the slab. This leads to the formation of unstable coating on the work rolls, which primarily consist of oxides (Al2O3; MgO), metallic Aluminium, and small quantities of carbon-containing compounds. This roll coating maintains its thickness by constantly releasing and reaccumulating particles and is thus transferred onto the slab surface. The morphology of the oxides depends on the alloy chemistry. The brazing quality is influenced by the coating of the hot rolled coil. If the flowability and wettability properties of the liquid filler are reduced during the brazing process, the quality of the brazing joint will suffer. This can lead to a higher number of rejects due to leakage or to inadequate results when the material is subjected to burst pressure and/or thermal shock tests. In order to meet demanding customer product requirements, AMAG TopClad®PURE is subjected to a surface cleaning process which removes most of the roll coating. This significantly reduces the amount of oxides and ensures optimum brazing results. This article presents a material characterization of AMAG TopClad®PURE and describes the advantages of this brazing sheet.

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