ZA-1: Addressing a Narrow Thermal Processing Window

January 26, 2017

Addressing the narrow thermal processing window is perhaps the biggest concern when considering an aluminum brazing project.  The problem, simply stated, is that the aluminum base metals melt at about the same temperature as the brazing filler metal.  The solidus temperature, the last temperature at which the alloy is completely solid, marks the point where damage begins to occur in the base metals.  The most standard BAlSi aluminum brazing alloy, 4047, has a melting range of 1070° – 1080°.  By comparison, 6061 and 6063 grades of aluminum have a solidus of 1100 and 1140 degrees respectively.  1100 and 3003 grades of aluminum have a higher solidus, 1190 degrees, but still presents a significant brazing challenge.

The availability of cesium fluxes and their low melting range (788°-842°) have ignited interest in Zn-Al brazing alloys.  Bellman-Melcor’s ChannelFlux® ZA-1 (78Zn 22Al) is specifically designed for use on thermal transfer devices.  The low melting phase of this alloy (826°-905°) is perfectly matched to the thermal activity of the Cs fluxes, providing a substantial thermal window for most aluminum brazing applications, especially for 6xxx aluminum.  Tensile strength and burst tests with 78Zn 22Al consistently show the braze joints demonstrate greater durability than the base metals, and saltwater spray testing to ASTM B117 for 2000h showed no signs of visible corrosion and no deterioration of mass.

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