VAC AERO Brazes Aluminum for Airborne Electronics

By: Vac Aero International  09-12-2011
Keywords: environmentally friendly, Brazing, Vacuum Brazing

When joining aluminum for aerospace electronics, brazing often is the most practical choice for creating a continuous all-metal joint interface. Because of its light weight and excellent thermal conductivity, aluminum often is the material of choice for assemblies that house or cool airborne electronics. These complex assemblies often are manufactured from numerous individual components that must be joined.

There are many ways to join aluminum including mechanical fastening (screws, rivets, etc.), adhesive bonding, welding and brazing. The selection of a joining process must be based on a careful analysis of the service requirements and the materials involved. For example, the joint’s mechanical strength is usually critical. A structural joint requires good tensile and shear strength as well as resistance to fatigue from cyclic vibrations. Furthermore, the thermal conductivity of the joint is essential in applications requiring heat dissipation. Brazing of aluminum can meet all of these requirements.

Vacuum brazed aluminum air-cooled heat

exchanger for airborne radar system.

 Vacuum brazed aluminum chassis panel

for defense avionics.

The traditional approach to brazing aluminum is dip brazing, where the assembly is immersed in a bath of molten salt that acts as a flux to promote braze alloy flow. It is the best brazing process for fabricating aluminum boxes or enclosures with long vertical joints. Because the salt supports the structure, the braze alloy tends to stay in the joint rather than pooling at a low point. However, dip brazing presents a significant risk of residual salt becoming entrapped in braze joints or hidden recesses within the structure. This can cause serious corrosion problems if the salt is subsequently exposed to moisture. A thorough post-braze cleaning operation is a necessity, usually involving large volumes of de-ionized water.  This is often followed by exposure to a humidified environment to try to leach out entrapped salt residues.

Vacuum brazing of aluminum does not involve the use of flux so eliminates any risk of corrosion.  It is also much more environmentally friendly than dip brazing. However, the process requires specially designed furnaces which must pump to harder vacuum levels than those required for many other vacuum brazing processes. The furnaces must have hot zone designs that permit rapid heating while maintaining excellent temperature uniformity. Many aluminum alloys are brazed at temperatures within a few degrees of their solidus temperatures. Careful control of ramp rate and temperature uniformity is essential to prevent melting of the base metal. Furthermore, brazing temperatures are below the red heat range where heating in vacuum becomes most efficient. As a result, hot zones must be designed with low thermal mass and sufficient heating element surface area. Aluminum vacuum brazing furnaces can also be equipped with gas quench systems to reduce cycle times.

Keywords: Braze Alloy, Brazing, environmentally friendly, Vacuum Brazing,

Contact Vac Aero International

Email - none provided

Print this page

Other products and services from Vac Aero International


Hot Zone Repair, Re-build and Retrofit

Besides catastrophic damage due to mechanical abuse, eutectic melting or braze alloy spillage, vacuum furnace hot zones will deteriorate over time as a result of the repeated thermal cycling to which they are exposed. Graphite-based insulation construction, including the use of modern carbon composite materials, usually lasts longer than metal-based construction.


Energy Optimization in the Heat-Treat Department

Specializing in vacuum heat treating and brazing for aerospace and other high-technology industries, VAC AERO International’s Oakville, Ontario, plant operates more than 24 vacuum, air and controlled-atmosphere furnaces. As North American electricity rates continue to rise, consumers are looking to new tech-nologies to control their energy usage and reduce costs.


Product/Services News

Specializing in vacuum heat treating and brazing for aerospace and other high-technology industries, VAC AERO International’s Oakville, Ontario, plant operates more than 24 vacuum, air and controlled-atmosphere furnaces. Savings can also be easily achieved by making slight changes to the timing of this consumption, thereby reducing the peak electricity demand.


VAC AERO Develops New Hybrid Vacuum Furnace Control System

VAC AERO’s latest advancement in vacuum furnace controls is a hybrid system based on the Honeywell HC900 controller for mechanical and thermal functions integrated with Honeywell Plantscape Vista for supervisory control and data acquisition. It also has extensive reporting capabilities and can generate reports in flexible formats including mathematical and statistical functions.


VAC AERO Specializes in Custom Designed Vacuum Furnaces

Maintaining vacuum integrity, temperature uniformity and process efficiency in these systems involve the innovative thinking and experience for which VAC AERO’s engineering staff is well known. VAC AERO has been involved in a number of projects that integrate complex work-handling systems into large vacuum heating chambers.