Fran D

iTrader: (5)

Anyone know where Al 356-T6 (stock cylinder head aluminum) sits on the Galvanic Table?

Thanks.

Fran D

iTrader: (5)

Anyone? This is Advanced Engineering Tech, right? I know that some of you guys work in the Aerospace industry, so you should have this info (since 356 is used in a lot of light aircraft bracketry). After all, I'm not asking how much horsepower a Kevlar pilot bushing will make!

Steve Bryant

iTrader: (1)

I have tried to do some research on the properties of A319 (used for blocks and some heads) versus A355 and A356 by talking to a couple of structural properties engineers at my company. One of them showed me a reference book with a bunch of graphs and charts, but very little text. Maybe I can talk to someone in metallurgy and learn more, but I'll have to find someone as I don't really know anyone who does this . . . yet. The AXXX Alpha numeric series is a designation for aluminum (Al) alloys well suited to casting. The T number is a temper number. For instance, T-0 is un-tempered like aluminum foil. It is very malleable and lacks suitable rigidity to be worth muck just as it is. Usually a part will be cast or forged and it will start it's life as a partially completed part in the zero state. Then, it may be tempered partially or fully by heat treating processes that give the alloy a more rigid state for machining and durability in use.

Regarding the galvanic table, are you worried about corrosion? In avionics (my gig), I think about galvanic proprieties regarding permissible coupling of metals related to dissimilar metal corrosion due to electron transfer of electrons from one element to another. There may be more than one type of galvanic table for all that I know right now. Please be more specific about the nature of your concern.

Steve

Fran D

iTrader: (5)

Exactly! Knowing that most Al alloys are highly anodic, I wanted to know where 356 sat. Certainly, with a cylinder head, it's easy to keep the cathode/anode ratio small with most steel fasteners. But, I'm particularly concerned with how aggressively it may attack an SS A2 or A4 fastener, especially with a larger, flanged area. Any insights you can provide are appreciated.

Steve Bryant

iTrader: (1)

Take a look at some of these search references http://www.google.com/search?sourcei...vanic+coupling. I would use anti-sieze compound as a barrier between fasteners, washers, etc. and move forward with your project. Regarding aluminum and corrosion, it's important to flush and change your coolant every few years slow corrosion internally. The coolant migrates to an ionic state due to contamination and chemical breakdown and it can even become a fairly good conductor of electricity. Contaminated coolant and an engine that is poorly bonded (grounded) to the frame and negative battery terminal can cause the interior of the coolant passsages to be eaten out like a hot water tank with an anode that is all used up.

My advice is to use the ant-sieze and move forward.

Steve

Fran D

iTrader: (5)

The anti-seize is a good idea, but by that I'm assuming you mean the non-metallic compounds? I know that Loctite sells a zinc-based anti-seize that is specifically designed for aluminum/ferrous interfaces. This always seemed strange because one would think the zinc would go nuts on the aluminum or steel surfaces, since it's near the top of the galvanic series. But, maybe that's the point?

The links were helpful, especially the anodic index table. Thanks.

Steve Bryant

iTrader: (1)

I've used graphite-based anti-seize compounds on lug nuts, spark plugs, all miscellaneous fasteners for engines, transmissions or any other mechanical parts not requiring something like an ARP Grease or if not using thread locking compound for about 35 years. In fact, I'm pretty sure that various forms of the stuff has been around since World War II. Locktite and many other manufacturers make it. There is a military specification (MIL SPEC) for the stuff, maybe more than one. The required torque values do not change with this product (unlike using a special purpose fastener assembly grease). If I install a water pump, exhaust manifold or anything else on an engine (cast iron or aluminum), I always use the stuff because I want to be able to take it apart in the future. I used to be a diesel truck mechanic, and I've had more bad experiences with fasteners galling, breaking, etc. than I care to mention. Anti-seize is an ounce of prevention and it minimizes if not entirely prevents dissimilar metal (galvanic) corrosion in my experience.

Steve

bwana

May not help but...Alcoa puts out a book, or used to, that had a variety of references across many disciplines of study, ie. electrical properties, how well it'd anodize, weldability, etc. It was a large technical book, say 400pp or so & was expensive, $150 10yrs or so ago.