Repaired a brake caliper

[Chris Stevens]

Almost all present automotive aluminium die castings have a fair amount of mag in them as this makes them stronger, which means they can be made thinner and at lower cost. Very easy to tell a casting with higher mag content as when you hit it with something, the sound will have more of a ring to it as the casting is harder.

Older Brit bike castings seem to have more Si, which makes them far easier to weld than the parts around currently. If strength is not an issue its probably a good idea to use Si rod even on later castings, as it tolerates dirty base metal a bit better, and is easier to use.

I tend to use 5356 for all castings though, as mixed mode on Hitachi seems to make castings much easier anyway.

 

[RichardM]

What was it off, looks Suzi to me?

 

[Pete.]

Kawasaki but I think it's just a generic nissin design same as many Suzukis use on the back.

 

[Member 66061]

Nice work, well done Good payment aswell

 

[hotrodder]

Almost all present automotive aluminium die castings have a fair amount of mag in them as this makes them stronger

Based on what evidence?

Mostly about other design considerations and fairly old (Carroll Smith passed away in 2003 and the article is probably from one of his books published in the '80s?) but towards the end specific alloys are mentioned and both the casting flavours are AlSi7Mg http://stoptech.com/technical-support/technical-white-papers/monobloc-vs-2pc-calipers
Brake caliper fatigue life study, same flavour of aluminium with plenty of Si and very little Mg http://link.springer.com/article/10.1007/s11661-004-0070-3
Two different flavours this time but both have plenty of Si and less than 1% Mg http://papers.sae.org/1999-01-0346/

When something stronger is desirable, especially for elevated temps service, the 2xxx series and AlSiCu alloys are where it's at these days... a319-t5 (AlSi6Cu4) or a380.2 (AlSi8Cu3) for cylinder heads for example. For aluminium disc mounting bells something like 2024 is not only stronger than a 6xxx series but retains it's properties to temperatures when a 6xxx or even 7xxx series has softened lots. http://articles.sae.org/10314/ is about a206 vs a356 for things like hubs and brake calipers

Very easy to tell a casting with higher mag content as when you hit it with something, the sound will have more of a ring to it as the casting is harder.

You can't identify mag content of a casting by hitting it with something

http://www.nortal.co.uk/LM5/ is an AlMg casting alloy with ~5% Mg
http://www.nortal.co.uk/LM25/ is an AlSiMg casting alloy with ~7% Si and less than 1% Mg. It's also one of the most common flavours used for castings aka A356.0

Note the hardness numbers in the links... in the 'as cast' condition there's very little between them with regards to hardness. Heat treat the LM25 and it ends up harder and stronger than LM5

 

[Chris Stevens]

I have been repairing automotive castings for more than 20 years now, and things like wheels sometimes have the material they are made from marked. Years ago I used to repair t wheels with 4043 rod, but found cracks in the weld were sometimes a problem. Changed from Si rod to alternative Mg material, and few if any problems now. Obviously not many castings are subject to the same sort of forces as wheels, and I guess Si rods are a better choice than Mg for most things as it much easier to get a good weld, and prep isnt as intensive?