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Soldering copper to aluminum

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  • #16
    The soldering process does not form a eutectic. The soldering alloy (not the base metals being joined) are eutectic. Eutectic merely means that an alloy of more than chemical compound that transitions from solid to liquid (and the reverse) at a single temperature. Non eutectic alloys solidify (or become liquid) in stages, at the solidus temperature of each constituent of the alloy. Because of this they have a plastic stage.

    Eutectic alloys are useful for soldering as they do not have a plastic phase. The transition from solid to liquid and back is a single specific temperature.

    The topic of whether or not soldering causes the solder alloy to alloy with the base metals is still debated. Some sources claim the joint is a "glue joint", while other claim the alloyed joint.

    So at this point, I don't think the science conclusively proves the glue joint or the alloy joint...

    Just my .02

    Jeff

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    • #17
      Harris sells an Aluminum solder kit:

      http://www.weldfabulous.com/Filler-M...-p5918946.html

      This works at normal soldering temps and will stick to a lot of things. It work especially nice for soldering Lithium Polymer battery packs since one terminal is aluminum and the other is iron. It is a Zinc-Tin solder with a special flux.

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      • #18
        Originally posted by JABoyce
        The topic of whether or not soldering causes the solder alloy to alloy with the base metals is still debated. Some sources claim the joint is a "glue joint", while other claim the alloyed joint.

        So at this point, I don't think the science conclusively proves the glue joint or the alloy joint...

        Just my .02

        Jeff
        Then what, in your opinion, causes a bare copper soldering gun tip to slowly disappear when used with lead-tin solder.

        Now, if you iron plate the tip, it seems to last nearly forever. Could it be that iron is nearly insoluable in molten lead-tin alloy while copper is just the opposite?

        RWO

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        • #19
          Originally posted by RWO
          Then what, in your opinion, causes a bare copper soldering gun tip to slowly disappear when used with lead-tin solder.

          Now, if you iron plate the tip, it seems to last nearly forever. Could it be that iron is nearly insoluable in molten lead-tin alloy while copper is just the opposite?

          RWO
          The casing you see on soldering iron tips are not iron, it's a silver/nickle alloy. An iron tip would never tin properly, if at all, and if you can't tin an iron it makes for very poor heat transfer and crappy solder joints.

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          • #20
            Originally posted by Tony
            Good tip!

            Just curious though, how does this soldered connection compare (electrically)
            to a mechanical connection? meaning using a small screw.. or perhaps drilling
            in the end of the aluminum rod, inserting the wire, and crimping it?

            Tony
            Two very unlike metals = electrolysis corrosion. Ask any boater.

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            • #21
              There are billions of mechanical copper to aluminum connections - electrical cables... rated devices simply use a plated surface on the connector and aniti-oxidant grease on the aluminum.

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              • #22
                The soldering process does not form a eutectic. The soldering alloy (not the base metals being joined) are eutectic.
                Not all solders are eutectics including not all tin/lead solders. So called "radio" solder is a eutectic alloy since the eutectic alloy of tin and lead is close to 60/40 ratio. A eutectic alloy also has the property of having the lowest melting point of any alloy ratio of two metals. Because of that when an alloy is formed by dissolving a higher melting metal in a molten lower melting metal a eutectic alloy is automatically formed.

                As for any "debate" regarding whether an alloy is formed, there isn't any debate in scientific circles. In order to solder at all the substrate must be soluble in the solder alloy and will form an intermetallic alloy at the joint.
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                • #23
                  It never occurred to me that there might be anything controversial about this subject.
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                  • #24
                    Originally posted by Chris S.
                    The casing you see on soldering iron tips are not iron, it's a silver/nickle alloy. An iron tip would never tin properly, if at all, and if you can't tin an iron it makes for very poor heat transfer and crappy solder joints.
                    You are wrong about iron plating. See http://www.all-spec.com/products/8125N.html

                    I know some tips are now nickle plated, but the original plating for long lived tips was iron. Haven't you ever soldered something made from steel? It's almost as easy as copper with the right flux.

                    RWO

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                    • #25
                      Regardless of the controversy, I'm glad to know that there's a product out there that will make soldering aluminum to copper easy.

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                      • #26
                        Originally posted by RWO
                        Then what, in your opinion, causes a bare copper soldering gun tip to slowly disappear when used with lead-tin solder.

                        RWO
                        In my experience that only happens with that crappy lead free solder,I won't use it anymore for that very reason.
                        Took me a while to realise that it was the lead free solder causing loss off copper from the bit.

                        Allan

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                        • #27
                          Some of the corrosion of the copper soldering tip is from galvanic action, some is from the acid in the flux, and some does end up alloyed into the joint.

                          The intermetallic bond is a result of the wetting. Surface tension and friction resist wetting. The interatomic attraction between the solder alloy and the base metal overcomes the resistance to wetting. While the metals at the intermetallic bond commingle, and form a very thin layer (1-3um) of substitutional alloy. Tin/Copper (SnCu) being the most common.

                          An intermetallic and substitutional alloy are not the same thing. Colloquially an alloy is a mixture of metallic elements in solution. Scientifically an alloy is a homogeneous mixture of metallic elements in solution. An intermetallic is not homogeneous.

                          On the other hand, there is also a colloquial defintion of intermetallic that can include all alloys. Complex, simple, homogeneous and non-homogeneous.

                          There are elements of chemical (atomic) bonding, and mechanical bonding of the crystal structures in the intermetallics of a solder joint. So many feel the bond to both an alloy and a "glue".

                          I guess the debate is not on the atomic structure of the solder joint, but on the terminology used to describe it. The definitions of "intermetallic" and "alloy", and how they overlap is where the debate is.

                          Just my .03

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                          • #28
                            Electrolytic corrosion

                            This is for a yagi aerial element as I recall, so presumably exposed to weathering. My concern would be electrolytic corrosion.

                            When aluminium first became available as a sheet at reasonable prices, a well known boat builder decided to make a lifeboat from it. He used the traditional coppr riveting that had worked so well for clinker built wooden boats. After launching and during tests they were puzzled by the fizzing sound and a little later by the spurts of sea water coming from the rivets !

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                            • #29
                              Originally posted by lakeside53
                              There are billions of mechanical copper to aluminum connections - electrical cables... rated devices simply use a plated surface on the connector and aniti-oxidant grease on the aluminum.
                              Yes, that can be done too.

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                              • #30
                                One of the problems of using a strictly mechanical connection is due to the dimensional constraints when dealing with gigahertz frequencies. There isn't room for a reliable physical connector that won't disturb the electrical properties of the antenna. The spacing of the elements, the dimensions of all parts and the connections to the driven element are all critical. For instance, to achieve close to the theoretical maximum gain the lengths of the antenna elements must be correct to within a tolerance of about +- .007".

                                Building such an antenna array isn't just a matter of bending up some wire. It actually becomes a machining exercise.

                                As for corrosion of the joints and the rest of the antenna it will be sprayed with clear lacquer for protection. I will post pictures of the antenna when I have something to show.

                                While on this topic does anybody have a suitable downconverter lying around that will work with a Yaesu FRG 7700 that they don't need and would like to trade?

                                The antennas are designed for the 1296 mhz amateur band.
                                Last edited by Evan; 11-04-2011, 04:35 PM.
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