What Is Aluminum Vacuum Brazing

Vacuum aluminum brazing requires a careful balance between time, temperature and vacuum. Control of these parameters determines the success of the basic brazing process, including charging, heating, brazing joint cleaning, solder melting and discharging.
Vacuum aluminum brazing is performed in a special working environment, requiring advanced controls to ensure rapid vacuuming to reduce oxygen content to ppm levels, and a specially designed vacuum furnace system to achieve excellent temperature uniformity.

Types of Aluminum Brazing
Aluminum brazing can be done with or without flux, and the join can be accomplished using many different methods.
In flux brazing, the flux flows to the joint and is displaced by the liquid solder flowing to the joint, thereby removing the oxides on the components and ensuring a reliable and strong joint. Flux comes in many different forms: paste, liquid or powder. Some electrodes are coated with flux, or the core is coated with flux, which can effectively apply the necessary flux during the brazing process. Flux brazing processes include torch brazing (manual or automatic), induction brazing, salt bath brazing (immersion brazing) and controlled atmosphere brazing (CAB).
Brazing performed in a vacuum furnace is considered fluxless brazing because it does not use flux in producing the joint. Fluxless brazing processes can be performed under inert atmosphere or vacuum conditions. Uses of these processes include, but are not limited to, semiconductor manufacturing, ceramic-to-copper bonding, etc. Due to cleanability under vacuum conditions, flux is not required. In the vacuum aluminum brazing process, magnesium is used as an additive or getter.

Advantages of vacuum aluminum brazing
Brazing has many advantages over other metal joining processes. Because brazing does not melt the base metal of the joint, tolerances can be more precisely controlled and a clean joint can be obtained that requires no additional cleaning. The meniscus (crescent shape) formed by the solder at the joint is an ideal shape to reduce stress concentration and improve fatigue performance.
Other advantages of vacuum brazing include:
Ability to join parts with very thin or thick sections.
Suitable for compact components with many joints that need to be sealed (such as heat exchangers) or components where the joints are deep and difficult to access
Able to join dissimilar metals, such as copper and stainless steel.
Suitable for manufacturing components with a large number of contacts.
In particular, vacuum aluminum brazing can significantly reduce component deformation due to more uniform heating and cooling compared to local joining processes. This type of brazing produces a continuous and tight joint. Components with large surface areas and a high number of joints can also be successfully brazed.
If hardenable alloys are used, hardening can also be carried out in the same furnace. The vacuum furnace system is equipped with a forced cooling system that can effectively shorten cycle times.
The reproducibility of vacuum furnace brazing results is extremely high because the key process parameters (i.e., vacuum level and temperature uniformity) remain consistent from batch to batch. After the furnace chamber starts to evacuate, the capillary channel at the joint (even if the channel is very long) can effectively discharge the remaining gas, thereby fully moistening the entire joint.
Vacuum aluminum brazing is ideal for materials that are prone to oxidation. Vacuum brazing is a flux-free process, which eliminates the problem of corrosive flux residues. The brazed parts have a clean surface with a matte gray finish. This process is basically pollution-free and requires no post-weld cleaning.

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