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LM24 versus LM2 for chrome plating

I am a quality engineer working in the automotive industry we are currently experiencing a high reject rate of chrome plated aluminium parts (LM24)due mainly from porousity in the casting. Would changing the base metal to LM2 give a better casting? and will LM2 plate as good as LM24?

Robert Turton
automotive - Birmingham, West Midlands, United Kingdom


Robert, Can you tell us more about the LM alloy buy the differents bettwen this aluminium alloy content's. To plate on casting alloys the problem is always the silicon contents. But if your plating shop use a chrome solution type SRHS or a Sargent's solution I can't not se any problem with that. But it easy'r to solve you questin if we have the alloy content's.


Anders Sundman
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,


Dear Anders

Sorry for delay with my response, we are still experiencing a high reject rate up to 80% after polishing and plating this is mainly due to the part design and high finish requirement. That is why we wanted to try a different material.
Currently we are using LM24
Cu 3-4 Mg 0.3max Si 7.5-9.5 Fe 1.3max Mn 0.5max Ni0.5 max
Zn3.0max Pb 0.3max Sn 0.2max Ti 0.2max Cr 0
Possible replacement LM2
Cu 0.7-2.5 Mg 0.3max Si 9.0-11.5 Fe 1.0max Mn 0.5max Ni0.5 max
Zn2.0max Pb 0.3max Sn 0.2max Ti 0.2max Cr 0
Do you think this could be an improvement ?

My plater does not know what chrome solution type SRHS or Sargent's solution is?

Robert Turton
- UK


Sergeant's chrome plating solution is also known as "conventional" chrome plating or "100:1" bath, Robert. This is the oldest of the chrome plating solutions and it uses sulphate as the catalyst in the ratio of 1 part of sulfuric acid to 100 parts of chromic acid.

Alternately to sulphate, or more likely in addition to it, fluoride catalysts can be used. The fluoride can be a very sparingly soluble material that, at least in theory, will dissolve into the plating bath at the correct ratio, with the excess precipitating as a sludge. This is known as SRHS or self regulating high speed. Good luck.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

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