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|PRODUCT DATA of 07: Filler materials|
|Material||07: Filler materials|
|General Information||Fusion joining techniques produce permanent joints. Soldered joints and some brazed joints can be disassembled with care.|
|Use in Spacecraft||Welding is a common fabrication method for metals used in spacecraft. Brazing usually refers to joining with alloys of copper, silver and zinc and should be used instead of soldering when stronger joints and an increase in temperature resistance is specified. Soldered joints are used for electrical and thermal conducting paths and for low mechanical strength joints. Soldering is commonly referred to as "soft-soldering" in which ow-melting point alloys, such as tin-lead or indium-based materials are used.|
|Main Categories||There are a large number of welding filler materials available. Forms (e.g. wires and rod) vary depending on the welding technique used. Selection of the correct filler rod is largely dictated by the metals being joined, notably alloy composition. Filler materials, welding procedures and post-weld processes are detailed in aerospace standards and specifications.
Comments on weld filler materials also apply to braze metals and processes. An added complication is that braze fillers are generally very different from the parent weld materials andso galvanic couples andother corrosion effects also need consideration.
Solder alloys that are acceptable for use inelectronic assemblies inspace, and their associated fluxes and process chemicals (e.g. solvents and cleaning baths), were subject to intense evaluation, see Table A-7 and Table A-8 (from ECSS-Q-70-08).
Solder alloys consist of the tin-lead and indium-lead alloys defined in ECSS-Q-70-08 and ECSS-Q-70-38. They are procured according to these specifications, they define purity levels and, where necessary, fluxes of suitable formulation for the assembly of spacecraft electronics.
|Processing and Assembly||Aircraft standardsandspecifications arenormally applied.Other critical industry sectors (e.g. nuclear and power-generation) can offer guidance on specialist materials.
Fusion joining processes are skilled operations and personnel shall have appropriate training and certification to produce the specified high-quality, reliable joints.
|Precautions||Not all metals and alloys can be joined by welding or brazing. Not only the weld itself (fusion zone), but the heat-affected zone and the unaffected parent (base) metals shall be considered.
Not all “industrial” welding techniques can be used on allmaterials. The choice of welding process is largely dictated by the metal composition, although the component itself and the ease of producing an acceptable weld are important, as is the correct selection of the fillermaterial. For some alloys preheating can be used to reduce thermal-distortion effects and post-weld thermal treatments to recover mechanical or environmental resistance properties.
The correct selection of parentmaterials andweldmethods requires consideration of all factors that affect operational capability of the parts concerned. Welding procedures are selected on their ability to provide the specified weld quality, minimum weld energy input and protection of the heated metal from contamination.
Comments specific to the welding of particular materials are included in the section on that material class.
For some fillermaterials additional qualitativeanalysisornon-destructive testing can be carried out (e.g. Ni-based filler rod) to ensure that the correct filler metal is used on each specific critical part.
Brazing is normally restricted to joints in structural parts that experience shear loading rather than tensile loading.
Fluxes used to producewelded, brazed or soldered joints can be corrosive and need to be removed thoroughly prior to post-joining processes (heat-treatment) and operation in service.Residues of chemicals or processes used for flux removal shall also be cleaned from components. Common soldering fluxes, their application and use are detailed in ECSS-Q-ST-70-08C.
|Hazardous and Precluded||Corrosive acid fluxes available for the pre-tinning of soldered joints can provoke stress corrosion cracking and general surface corrosion of component leads or terminal posts. Their general use is therefore restricted and precise control of the flux-removal processes shall be applied.|
|Some Representative Products||There are numerous suppliers of welding and brazing consumables (e.g. fillers and fluxes) in Europe. Solder alloys can be procured from ELSOLD GmbH & Co. KG.|