F.A.Q.
Material and Material Impact
Which Materials are Suitable for Dip Brazing?
Not all aluminium alloys are suitable. A high alloy content in
certain materials can limit the solderability. The composition of the alloy should be of the type AlMgSi. For example EN-AW 6082 and
EN-AW 6083. Pure aluminium also works without issue.
How is the Material Impacted by the Process?
The strength of the core material is affected by the brazing process. Heating the material close to the melting point results in the material assuming properties corresponding to the annealed state. After a couple of days spent at room temperature, curable materials will regain a part of their original properties.
To further increase the strength of the curable alloys the material can be heat treated and aged.
To further increase the strength of the curable alloys the material can be heat treated and aged.
Dip Brazing Technology
What is the Salt Bath Composed of?
The salt bath is composed of potassium, sodium and lithium chlorides
as well as a small amount of various fluorides.
The salt is heated with the help of electrodes to approx. 595° C while brazing. The salt melt acts both as a heatsource and as flux in the brazing process.
The salt is heated with the help of electrodes to approx. 595° C while brazing. The salt melt acts both as a heatsource and as flux in the brazing process.
How Big can the Components be?
The salt bath soldering ovens dimensions dictate the maximum size. Alumbra has two ovens.
Their measurements are: 1000mmx1000mmx800mm and 1200mmx800mmx800mm.
The usable brazing dimensions are slightly smaller as the brazing fixture requires some space.
The usable brazing dimensions are slightly smaller as the brazing fixture requires some space.
Are Further Tools or Fixtures Required?
By designing the components so to be self-fixing, we avoid the use of fixtures. This has multiple benefits:
• Cost of construction and manufacturing of fixtures can be avoided.
• Maintenance of fixtures due to wear and tear is eliminated and if the component undergoes reconstruction new fixtures do not have to be fabricated.
• Heating and cooling times of heavy fixtures are excluded which reduces the processing time
• Multiple components can fit in one brazing batch.
• Lower weight and therefore easier handling of a brazing batch.
With some components fixation aids or fixtures are unavoidable. The fixtures used in this case are made of aluminium alloys or stainless steel. To prevent the joining of aluminium fixtures to the components being soldered these fixtures are anodized. In such cases there are many options available to us for the successful soldering of the work.
• Cost of construction and manufacturing of fixtures can be avoided.
• Maintenance of fixtures due to wear and tear is eliminated and if the component undergoes reconstruction new fixtures do not have to be fabricated.
• Heating and cooling times of heavy fixtures are excluded which reduces the processing time
• Multiple components can fit in one brazing batch.
• Lower weight and therefore easier handling of a brazing batch.
With some components fixation aids or fixtures are unavoidable. The fixtures used in this case are made of aluminium alloys or stainless steel. To prevent the joining of aluminium fixtures to the components being soldered these fixtures are anodized. In such cases there are many options available to us for the successful soldering of the work.
What is the Solder Material Made of?
The solder material is made of aluminium with a high silicon content. Roughly 12% Silicon is used to lower the solder's melting point. Solder is available in the form of thread and foil in a variety of dimensions, as well as in powder form.
Solder plated aluminium sheets of different thicknesses are also available.
When the solder melts and is pulled into the joint by capillary action it displaces the salt whereupon some of the material diffuses slightly between base material and solder. An exchange of material occurs and the joined components fuse together forming a strong joint. The effect of the heat treatment is negligible as it is not curable. The tensile strength, Rm, of the joint is between 100-110 N/mm².
When the solder melts and is pulled into the joint by capillary action it displaces the salt whereupon some of the material diffuses slightly between base material and solder. An exchange of material occurs and the joined components fuse together forming a strong joint. The effect of the heat treatment is negligible as it is not curable. The tensile strength, Rm, of the joint is between 100-110 N/mm².
Are the Materials Corrosion Properties Affected?
The salt is very corrosive but completely water soluble. To avoid corrosion issues all the salt remains are removed via careful, multiple step cleaning in hot water. The method therefore does not affect the corrosion properties of the material.
As the corrosion properties of the solder is close to that of AlMgSi there is good corrosion resistance and no risk of galvanic corrosion.
As the corrosion properties of the solder is close to that of AlMgSi there is good corrosion resistance and no risk of galvanic corrosion.
What Level of Precision and Tolerance does the Method Provide?
Before brazing the components to be joined are cleaned to remove dirt and grease and then any oxide layer that covers the components is removed. This is done through degreasing and bathing in sulfuric acid and nitric acid. This chemical bathing and then salt bath's fluxing properties do, to a minor degree effect the dimension of the starting material but the effect is marginal (max 0.02mm).
After brazing the parts are air cooled. Depending on the design of the construction and the composition of the components the cooling process can vary. This can in some cases lead to some shape change. These changes can generally be subsequently corrected.
The level of dimensional accuracy that can be achieved with this method is dependent on the design of the part as well as how many joints affect the desired measurements accuracy. The following example gives an indication of the method's potential accuracy. Suppose we join a box with 4 sides and a base with dip-brazing. Its dimensions are 100mmx100mmx100mm. We can expect a result with an accuracy of around 0.2mm-0.3mm in width and height. Generally, accuracy requirements down to 0.2mm-0.3mm can be placed on sheet metal construction whilst measurements down to 0.05mm arising from cutting processes are tolerated in construction.
After brazing the parts are air cooled. Depending on the design of the construction and the composition of the components the cooling process can vary. This can in some cases lead to some shape change. These changes can generally be subsequently corrected.
The level of dimensional accuracy that can be achieved with this method is dependent on the design of the part as well as how many joints affect the desired measurements accuracy. The following example gives an indication of the method's potential accuracy. Suppose we join a box with 4 sides and a base with dip-brazing. Its dimensions are 100mmx100mmx100mm. We can expect a result with an accuracy of around 0.2mm-0.3mm in width and height. Generally, accuracy requirements down to 0.2mm-0.3mm can be placed on sheet metal construction whilst measurements down to 0.05mm arising from cutting processes are tolerated in construction.
Are Finished Surface Treatment Options Affected by the Brazing Process?
Surface treatment options are not affected by the brazing process although if you require a cosmetic anodizing finish some patchiness may occur in and around the joint.
This due to the increased silicon content of the solder and can result in the joint having a slightly darker tone than the base material.