[OT] soldering mild steel sheet, galvanic corrosion?

[Allen Mulvey]

Try to find an old time auto body man. He will be able to tell you
everything you want to know. My father used to solder the replacement panels
on cars. Back then the bodies were tin plate rather than galvanize. He had a
couple of blowtorches (gasoline) heating some large "coppers" which he
rotated through for the actual soldering. I still have a can of "Nokorode"
flux that he used. He also had a couple of acid based fluxes but I don't
know how he picked the right one for the job. Most of his solder was 60%
lead and 40% tin. I used to borrow it for electronic projects.

Unfortunately my father died several years ago so I cannot ask him about it.

Allen
Ps: Sorry Bob I keep forgetting to remove that tag.

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of
Jason White
Sent: Tuesday, June 16, 2020 6:39 AM
To: Microcontroller discussion list - Public.
Subject: [CAUTION: Failed DKIM Test][OT] soldering mild steel sheet,
galvanic corrosion?

Hi everyone,

I'm researching soldering/brazing thin steel sheet metal for a hobby
automotive project. (as an alternative to welding and spot welding*) The
purpose to is create a mechanical joint on a floor panel. The mechanical
joint will be subject to road salt spray.  I am trying to predict the
effects of corrosion.

As far as I can tell the type of sold/braze can have a big impact on
galvanic compatibility. Leaded solder looks fairly close to mild steel on
the "anodic index", I can't find any information for tin solder, and silver
based solder and bronze braze appear to be far away (promoting corrosion).

Does anyone have any input on the best solder/braze chemistry from a
corrosion perspective on mild steel?


*currently am not equipped with the correct welding equipment for sheet
metal, but am equipped to solder/braze.


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Jason White
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[Sean Breheny]

Hi Jason,

On Tue, Jun 16, 2020 at 5:25 PM Allen Mulvey <[hidden email]> wrote:

> Most of his solder was 60%
> lead and 40% tin. I used to borrow it for electronic projects.
>

Is that a typo? The eutectic point is at 60% tin, 40% lead (typical
electronics solder).

Sean
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[Bob Blick-5]

Interestingly, though, solder used for plumbing, sheet metal and other large mechanical things like stained glass is rarely 60/40 like electronic solder. The difference between it and 50/50 when it comes to workability is dramatic. 60/40 solder is harder to use in those applications because the whole workpiece melts at once, whereas with 50/50 you can work a section and have it fluid or slightly plastic, right next to an area that is still solid. There is a certain hysteresis to it that makes it more desirable in that application.

Best regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Sean Breheny
Sent: Tuesday, June 16, 2020 10:03 PM
To: Microcontroller discussion list - Public.
Subject: Re: [OT] soldering mild steel sheet, galvanic corrosion?

Hi Jason,

On Tue, Jun 16, 2020 at 5:25 PM Allen Mulvey  wrote:

> Most of his solder was 60%
> lead and 40% tin. I used to borrow it for electronic projects.
>

Is that a typo? The eutectic point is at 60% tin, 40% lead (typical
electronics solder).

Sean


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[Sean Breheny]

The behavior you mention is characteristic of all non-eutectic mixtures.
They have two "melting points" - a solidus point and a liquidus point. The
properties of the semi-molten mixture in-between those two points is quite
strange and typically some minimum force is needed to cause flow (unlike a
liquid), but there is no elastic region (unlike a solid).

Sean


On Wed, Jun 17, 2020 at 10:03 AM Bob Blick <[hidden email]> wrote:

> Interestingly, though, solder used for plumbing, sheet metal and other
> large mechanical things like stained glass is rarely 60/40 like electronic
> solder. The difference between it and 50/50 when it comes to workability is
> dramatic. 60/40 solder is harder to use in those applications because the
> whole workpiece melts at once, whereas with 50/50 you can work a section
> and have it fluid or slightly plastic, right next to an area that is still
> solid. There is a certain hysteresis to it that makes it more desirable in
> that application.
>
> Best regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of Sean
> Breheny
> Sent: Tuesday, June 16, 2020 10:03 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [OT] soldering mild steel sheet, galvanic corrosion?
>
> Hi Jason,
>
> On Tue, Jun 16, 2020 at 5:25 PM Allen Mulvey  wrote:
>
> > Most of his solder was 60%
> > lead and 40% tin. I used to borrow it for electronic projects.
> >
>
> Is that a typo? The eutectic point is at 60% tin, 40% lead (typical
> electronics solder).
>
> Sean
>
>
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>

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[Bob Blick-5]

Yes, I was familiar with that, just wanted to relate to how it feels to work with two different choices.

If you are making floor panels, 50/50 solder might be a better choice than 60/40. My experience with the two solders has mostly been with joining seams in horn antennas and EMC immunity chambers.

Friendly regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Sean Breheny
Sent: Wednesday, June 17, 2020 12:41 PM
To: Microcontroller discussion list - Public.
Subject: Re: [OT] soldering mild steel sheet, galvanic corrosion?

The behavior you mention is characteristic of all non-eutectic mixtures.
They have two "melting points" - a solidus point and a liquidus point. The
properties of the semi-molten mixture in-between those two points is quite
strange and typically some minimum force is needed to cause flow (unlike a
liquid), but there is no elastic region (unlike a solid).

Sean


On Wed, Jun 17, 2020 at 10:03 AM Bob Blick  wrote:

> Interestingly, though, solder used for plumbing, sheet metal and other
> large mechanical things like stained glass is rarely 60/40 like electronic
> solder. The difference between it and 50/50 when it comes to workability is
> dramatic. 60/40 solder is harder to use in those applications because the
> whole workpiece melts at once, whereas with 50/50 you can work a section
> and have it fluid or slightly plastic, right next to an area that is still
> solid. There is a certain hysteresis to it that makes it more desirable in
> that application.
>
> Best regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of Sean
> Breheny
> Sent: Tuesday, June 16, 2020 10:03 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [OT] soldering mild steel sheet, galvanic corrosion?
>
> Hi Jason,
>
> On Tue, Jun 16, 2020 at 5:25 PM Allen Mulvey  wrote:
>
> > Most of his solder was 60%
> > lead and 40% tin. I used to borrow it for electronic projects.
> >
>
> Is that a typo? The eutectic point is at 60% tin, 40% lead (typical
> electronics solder).
>
> Sean
>
>

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