It depends on what type of metal is used for the die casting.

If the metal used is zamac, I don't think it is possible to solder to it.  In fact it would not surprise me if the zamac melts at a lower temperature than most solders.  If the diecast is brass, then soldering should not be a problem, but most die cast model railroad stuff is zamac, I think.

soldering to zamac

Plating Tool?

MRH sponsor Micro Mark sells a plating tool intended for use with zamac.  It deposits a thin layer of copper which then should allow you to solder on top of the plating.   http://www.micromark.com/Copper-Plating-Kit-For-Die-Cast-And-Steel,8419.html 

I haven't used the tool, I just remember seeing it in the catalog.

Thank you

Thanks to all for the quick responses.  I buy a lot from Micromark, and I usually find their products rather good.  I think I am going to give their plating solution a try.  I will follow up with a further post, reporting on the results. 

Try adding a brass screw

I've never had any real luck soldering to zamac, pot metal, or anything else that locomotive frames (or Atlas frogs, seemingly) are made of.  What I do is to drill a small hole, tap it, and insert a brass screw.  I cut that off flush with the surface, and solder to the screw.  The brass takes solder nicely, and the threads make a good mechanical and electrical connection with the rest of the piece.  If I'm working in a blind hole, I'll frequently jam the screw too deep into the hole, sometimes even breaking off the head.  I want it stuck in there tight.

Ken

A Simple and Great Idea, Ken

I certainly could have used your idea years ago when I was trying to "super-detail" MDC and Tyco locomotives with an Air Pump!   IMHO this idea would be much stronger than the plating method.

Peter

success?

The problem is the heat melts the metal before the solder.  I don't think plating with copper would stop that.

I suggest that before you choose a method you visit Rickety Rails at http://www.ricketyrails.com/   They sell several grades of low temperature solder.  You can rig your iron on a light dimming switch to control its temperature  and experiment a little.  It takes a fine touch but can be done.  I built a critter railing this way - connect the hi-temp pieces first then add the medium temp then finish up with the low-temp.  I wouldn't want to super-detail a whole zamac boiler but for repairing and a few touches it be useful.

Art

Soldering Zamac

I had a Pen Line zamac engine that had been dropped and had a chunk missing from the roof.  When I tried to solder a piece of brass over it as a repair, the zamac melted before the tix low temp solder.  I just mad a larger missing piece.  I eventually used epoxy to glue the brass sheet in place.  That was 20 years ago, and it still looks good.

Kent in KC

nvrr49.blogspot.com

Carr's Solder & Fluxes

For zamak alloys.

Zamak Alloy Grades and Soldering Update...

It seems that manufacturer's use of Zamak brand metals is almost like "planned obsolescence" for some vintage models parts made from this alloy.  The problem is that just looking at a Zamak casting cannot show if the casting was made with correct materials and methods that is durable or if the casting material was contaminated and will eventually crumble.

There are several Grades of Zamak alloy metal available and my vintage O-gauge Ajin locomotive drive casings were made from Zamak - 3 alloy.  Pure Zamac material castings can be very durable, but any Lead metal contamination in a Zamac casting will start deterioration that causes Zamak to eventually crumble.  Re-casting or re-using older batches of Zamak alloys may also cause alloy impurities which lead to Zamak parts breaking apart easily.  A *possible* way to slow this deterioration is by using a Chromate Conversion Coating, but I have not tested this method.

The only Zamak soldering materials supplier I have found in the USA for Carr's C1003 179 deg C (354 deg F) solder is International Hobbies in California. As of Dec 2013, their website price for Carr's C1003 179 deg C solder seems to be around $11.  However, also needed is Carr’s C1032 Grey Label Flux 15ml. $19.95; for soldering Aluminum (No. 179 solder) and Mazak (die cast alloy).  I do not know where to purchase Chromate Conversion Coating material and have no specific recommendations.

Remember, Zamak is an alloy segmented by grades with an AVERAGE 179 deg C (354 deg F) medium to low melting point affected by the materials used in the original casting.  Conventional soldering equipment used to heat the C1003 solder may have problems consistently regulating soldering tip to exactly 179 deg C.  I have not had good luck using a microtorch for Zamak repairs.  Instead, I choose to use an American Beauty digital soldering unit with a single tip (not a resistance soldering unit) because I get more consistent temps and can more easily calibrate/check soldering temp settings with a IR tenp gun.  Any brand new digital soldering unit can be quite expensive, but eBay sometimes has decent used digital soldering unit prices.

"eventually used epoxy to glue the brass sheet in place"

that would probably be the best way to attach most parts to a zamak casting. If it needs more strength or electrical contact drill a hole and put in a metal pin......DaveB

Soldering to Zamac

Sorry I'm late to the party.  I remember the article David references but not the specific issue.  The idea was to take a dremel grinding tool and "gunk" it up with regular solder.  Then use that "gunked up" grinding tool to mechanically abrade the solder onto (and into) the Zamac boiler thereby creating a solderable surface "patch" . 

I've never used this technique...I just epoxy the part into the drilled (or pre-drilled) hole.  My favorite epoxy for this app. is JB weld. 

Why not just epoxy?

Just curious - I've always just used epoxy to affix to a die cast boiler.  Most detail parts have a "pin" just drill a small hole for the pin and epoxy in place. If no "pin" I drill a hole in both the detail part and the boiler, and use a small piece of brass wire as a mechanical connection between the parts as I epoxy in place.  Never had issues with breakage...