There is this from practical welding-
CASTINGS The most common casting alloys by Far are the AlSiMg heat-treatable castings such as A35G and A319. The correct filler metal for the 3XX casting alloys is 4043. If you don't know what the casting alloy is, it is logical to assume that it is a 3XX alloy. Again, this isn't foolproof. I would estimate that 90 percent of the castings you see will be 3XX alloys, but 5XX casting alloys are also somewhat common, These are non-heat-treatable and should be welded using 5356. Unfortunately, there is no easy way to tell a 3XX casting from a 5XX casting. Well, I don’t uppose any of this information is scientific, but hopefully it will allow you to make a more informed filler metal choice the next time you are confronted with this dilemma.. I have had good luck welding castings on C&C’s with 5356. Obviously you will have to pull your mast to repair this. Then I would look for softness under it t see why it cracked in the first place. Or you can make up a SS plate and not worry about the cracking.. Bill Coleman Entrada, Erie, PA From: Todd Williams via CnC-List [mailto:cnc-list@cnc-list.com] Sent: Friday, October 22, 2021 11:39 AM To: Stus-List Cc: Todd Williams Subject: Stus-List GelCoat Color Matching and Cracked Mast Step Well, yesterday, the boat was hauled out for the winter... time to get busy before winter sets in for Upstate NY. We had a great summer of sailing on our new to us 1980 C&C34 which we named Indigo Out We Go. 1 - There are some chips in the gelcoat, especially around the perimeter of the transom. What is the best way to go about color matching my beautiful blue gelcoat? Is this a factory color that I can reference by name or number at a marine supply store and get tinted? (See Photos for nice blue color) 2 - I bought Indigo with a cracked mast step plate. We sailed all summer with it, even up to 25+ knot gusts. I see no evidence of movement. I called an aluminum welder and he told me it would be tough to adequately reconnect the plate without knowing the alloy and grinding down the plate so the keelbolt doesn't crack it again (not sure if that is the original cause). Should I be concerned with this crack? Where am I likely to find a replacement part? (See Photos) PHOTOS - https://photos.app.goo.gl/XNxxNMUeBmkdUkyHA Thanks for the information on various threads all summer, I have learned a lot! TODD Sodus Bay, NY
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