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Aluminum vs Magnesium

adam_g

adam_g

Contributing Member
In very clean fresh water is m

In very clean fresh water is magnesium preferable to aluminum for sacrificial anodes?
 
"it will give better protectio

"it will give better protection. alum is for brackish water, and zinc is used in salt. the magnesium would work there too, but would go away very quickly, and leave you with no protection."
 
"The magnesium will be more ef

"The magnesium will be more effective in protecting the base metals, but will go away significantly faster... plan on repalcing them pretty soon if you store the boat in salt water.

The ion concentration of fresh water is significantly less than that of seawater, therefore the need for (and effectiveness of) sacrificial anodes is greatly reduced.

However, if the base metal (the metal you're trying to protect), is the same material as the sacrificial anode, there will be no galvanic potential. The anode will corrode at the same rate as the base metal, providing no protection. But, as mentioned above, in fresh water, it doesn't matter a whole lot anyway... if your drive is made of aluminum, you're just as well off with no sacrificial anodes as you are with aluminum.
In salt water, galvanic protection is a must.

Go here for more info:
http://www.engineersedge.com/galvanic_capatability.htm"
 
"David,
Just read the July 20

"David,
Just read the July 2007 issue of Boat US. The "ask chuck" section on page 30 and 31 talks about this. Chuck had come back with an oh by the way to recommend magnesium and/or aluminum in fresh and brackish water.
I agree the aluminum won't crust over like zinc, but as I mentioned above, it won't do anything to protect the aluminum base metals... there has to be disimilar materials for a sacrificial anode to do it's thing."
 
"If this helps, I use mag to p

"If this helps, I use mag to protect my aluminum boat in fresh water.

Jeff"
 
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