Soldering and brazing of aluminum (2)

Soldering and brazing of Aluminum

2

Common Processes Soldering

Brazing

Braze welding

Soldering

Soldering Aluminum• What is soldering ?• Soldering is by definition a low temperature joining process. Therefore,

less distortion of the aluminum component is expected by soldering than by brazing, welding or other fusion joining processes.

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Soldering

• Solder is divided into two categories;– Soft– Hard

Relies upon capillary action.

Describe soft soldering?

How is hard soldering different from soft soldering?

What is capillary action?

What are the requirements for capillary action?

Soldering Process1. The joint area is cleaned and fluxed.2. A heat source is used to raise the

temperature of the base metal above the melting of the filler metal (<840 oF).

3. The filler metal is added to the joint. Filler material should melt from the

heat of the metal, not the heat source.4. The filler metal flows into the joint and

adheres to the surfaces.5. The heat source is removed and the filler

metal solidifies, bonding the surfaces together.

• Typical applications of aluminum soldering:• heat exchanger assembly, electronic/electrical capacitor

manufacturing, and light bulb manufacturing. • None of these applications requires high tensile strength, but,

they do require the solder to not cause galvanic• corrosion over time.

Appropriate solders for Aluminum

• -Soldering requires proper heat on the component, not on the solder. Because of the highthermal conductivity and reflectivity of aluminum, it has been found that neither oxy-acetyleneflame torch, plasma arc, laser, induction heater, nor thermal spray is capable of providing goodresults.

• -high density infrared source of 300kWplasma lamp has been demonstrated to have successful results with 80 wt% Zn- 20 wt%Al andflux at a soldering temperature of 490°C.

• Mechanical tests showed that the joint area is strongerthan the parent material with minimum softening.

Temperatures and stresses• Soldering temperatures of 225°C to 490°C are well below the 661°C

aluminummelting temperature although 490°C is above most annealing temperatures.

• -Stresses in the aluminum from shearing, drawing, and heat-treating are changed by the localized heatingencountered during soldering and distortion may result.

• HEATING METHODS:-• -open flame cannot be considered• -Plasma Arc wire feed equipment on aluminumPanels :it was observed that the

heat is solocalized that neither soft, nor hard solders could flow consistently well between both panels.

• -Preheatingbetter capillary flowbetween the panels, hot cracking became evident in some samples due to the rapid buildup ofheat from the plasma arc.

• -Induction provides a rapid, delocalized heating technique for even large parts. Unfortunately,induction heating did not provide sufficient heat to melt the solder

• Both tin-based and zinc-based alloys have also been tried using the thermal spray to deposit on aluminum body panels as well as galvanized steel. This process does not enable solders tocapillary or flow between panels.

Simplified steps for soldering aluminum: Steps

• 1-For some difficult to solder and large surface area joints, it may be extremely helpful to pre-tin the joint area on each part with the solder before setting up to join the parts. Simply follow the steps below to coat the joint area of each part with an even coat of solder. Then, after the parts have cooled, follow the steps again to join the parts. The 1-2-3 rule applies here as well. Do not pre-tin one day and solder the next. A fresh oxide-free surface is important to soldering success. Pre-tinning your parts with the right solder can greatly improve joints on difficult to solder metals and large surface area parts.

• 2-Pre-clean the parent metal or metals to be joined. Prepare aluminum surfaces with a stainless steel wire brush. Breaking the tough aluminum oxide coating on the aluminum parts is the secret to aluminum soldering. These barriers reform quickly, so agitate, flux and solder in a rapid sequence.

• 3-Apply the appropriate aluminum soldering flux to break the oxide barrier and draw the solder into the joint/repair area. You may easily use the solder rod to spread the flux

• 4-Use a soft flame, heat gun or soldering iron to heat the parent metal adjacent to the repair area. A direct flame on the repair area is likely to overheat the solder and flux. If using a torch, hold the torch tip 4 to 6 inches away from the parent metal. If it is necessary to apply the flame directly to the rod or flux, pull the torch tip back even farther from the work surface and keep it moving.

• 5-The flux will begin to bubble and turn light brown. Besides preparing the parent metal for the solder, these changes indicate the proper working temperature for the flux. If the flux turns black, let the area cool, clean it & start over.

• 6-When the flux bubbles and turns brown, it is time to apply the rod. Drag the rod over the area to be soldered, until it begins to flow. Once the solder starts to flow remove the heat. If additional layers are needed, continue to drag the rod over the area. With some applications, for example with very thin wires, it may be helpful to tin the aluminum surface with the rod before soldering the parts together. In this case, follow steps 1 through 5 to apply an even coat of solder to the aluminum parts. Let these parts cool, and then follow steps 1 through 5 again, soldering the parts together. This will often result in a more consistent solder joint for small parts.

• 7-Observe the solder deposit. The solder should bond smoothly

• 8-Remove the excess flux with warm water and a wire brush. Flux residue is acidic and should ALWAYS be removed, even for “No Clean” fluxes.

Notes :• -The quality of the interface increased with increasing temperatures• -Do not overheat. The rod will melt if overheated, but will not bond properly. (Really cannot

emphasize this enough. Soldering is a low heat process designed so that the electronic parts and base metals are not damaged during joining.)

Brazing

Aluminum Brazing

IntroductionSoldering and Brazing are joining processes where materials, similar or dissimilar, are bonded together using a heating method and a filler metal without melting the base materials. The filler metal melts, wets(flowing of filler metal) the base materials, and subsequently flows by capillary action. Wetting of the base materials by the filler metals is enabled by the use of a suitable flux or

by acoustic vibrations .

Aluminum Brazing• Heavy metal brazing alloys cannot be used for brazing

aluminum due to the melting point of aluminum and its alloys and due to the required corrosion resistance of the brazed joint. As a result, brazing alloys based on aluminum, containing no or very small quantities of heavy metals and at least 70% aluminum, are employed. Most commercial filler metals are based on AL-SI system with silicon contents in the range 7-12% . In addition to a suitable brazing alloy, for brazing one also requires a medium which removes the surface oxide from the base material and keeps this surface bare during the brazing procedure. As well as fluxes, a vacuum is also considered a medium .The non-heat treatable alloys that have been brazed most succefully are the 1xxx and 3xxx and the low-magnesium members of 5xxx . of the heat treatable alloys only the 6xxx.

How to braze Aluminum?

• Knowing how to braze aluminum can be a useful skill for anyone who is faced with a variety of at-home repairs. Brazing aluminum is a quick and inexpensive option for repairing leaks, cracks, or holes in aluminum and is often found in air-conditioning repairs. When compared to welding equipment, aluminum brazing equipment is inexpensive, portable, and does not require high amounts of voltage.

Steps1-Wear non-flammable clothing, gloves, and safety goggles before

you begin the brazing process.

2-Clean all dirt, oil, paint, or other residue from the area to be repaired by aluminum brazing. Use a degreasing solvent to get rid of oil and grease.

Depending on the size of the repaired area, you may need to sandblast the area or use an emery cloth, grinding wheel, or file.

3-Clamp or support the piece to be brazed

4-Use a brush to apply the flux appropriate to the temperatures and the metal. An all-purpose flux covers a wide range of temperatures and is beneficial to have on hand for general purpose brazing. Add flux by dipping the filler rod into the flux. You may also use flux-coated rods to eliminate this step. The flux-

coated rods apply the flux during the aluminum brazing process.

5-Heat the repaired area with a propane or acetylene torch until the aluminum shows an orange bloom. This happens when the metal gets very hot. Once you apply a flux, it should change colors or turn clear throughout.

6-Apply the filler metal by running a brazing rod along the crack or the joint. The heat of the metal will melt the filler into the area needing the

repair. Move the flame of the torch on and off as needed to melt the rod.

7-Remove the flux after the filler material has solidified by dipping the part or pouring hot water on the repair. The flux will flake off. If it does not come off, use a wire brush to gently scrub the brazed area while wet or still in the

hot water.

8-Polish the area with an emery cloth after the metal has cooled completely.

9-Coat the area with a rust-resistant coating if you are not immediately finished with the area.

Methods of removing the oxide layerVacuum brazing

• The coefficient of expansion of aluminum is about three times as great as that of aluminum oxide. That’s why the oxide layers crack up on heating and the liquid brazing alloy can pass through these cracks down to the bare base material. The aluminum oxide layer becomes mechanically detached. Oxidation of the aluminum in the cracks during the heating phase can only be prevented if the atmosphere is completely devoid of oxygen.

• Using fluxes :- • flux is required to prevent oxides from forming while the metal is heated.

The flux also serves the purpose of cleaning any contamination left on the brazing surfaces. Flux can be applied in any number of forms including flux paste, liquid, powder or pre-made brazing pastes that combine flux with filler metal powder.

Brazing techniques• Flame brazing• In flame brazing, the components are heated to brazing temperature with

the burner Natural gas, sewer gas, propane and acetylene are used as fuel gases. The fuel gases are combined with drawn-in air compressed air and occasionally also with oxygen .In manual burner brazing, the area of the component to be brazed is applied with flux. For brazing bulk quantities of items ,burner-heated brazing machines have been increasingly used in recent years.

• Induction brazing• Induction brazing of aluminum is virtually only used

for brazing compensating bases. The brazing of compensating bases involves connecting an aluminum plate to a chromium-nickel steel cooking pot.

• Open furnace brazing:-• The brazing joints are wetted with flux and then the

component is passed through the furnace. As the brazing is carried out in air, a corrosive flux must be used for this brazing process.

• Furnace brazing under controlled atmospheres:-• reduction of the aluminum oxide layer is not possible at

brazing temperature even in pure hydrogen. It is hence necessary to use fluxes, even in inert gas atmospheres. However, only the non-corrosive type are employed. The most commonly used inert gas is nitrogen although nitrogen/hydrogen mixtures are also used.

Brazing Joints• The tensile strength of brazing filler material

is less than steel.• The strength of the weld is increased if the

joints are modified to increase the surface area.

Tensile strength of brazing rod is ~40,000 psi.

Tensile strength of steel electrode is 36,000 to 50,000 psi.

Reference1. Brazing aluminum

W. Kohlweiler , Braze Tec GmbH, Hanau2.the Copper Development Association.3. The Harris Products Group

www.harrisproductsgroup.com

Presented to:-

DR/ Eslam El Galy

Thanks