Henkel Corp., www.henkelna.com
Volvo Penta, www.volvopenta.com
Complying with two sets of environmental regulations while making a high-end product that appealed to an exacting customer base was a challenge to designers at marine-engine maker Volvo Penta, Chesapeake, Va. Fortunately, they found a solution that let them exceed customer expectations and go green at the same time.
Volvo Penta’s Ocean X stern drive and engine exhaust for 20 to 35-ft pleasure craft needed to be low maintenance and lightweight. Lighter boats can rapidly accelerate and plane out — skimming across the water instead of plowing through it — for better fuel-efficiency and at higher top speeds. Previous Volvo stern drives used aluminum to cut weight and a chromate coating to combat seawater’s corrosive effects.
However, chromate is a carcinogen regulated by the Environmental Protection Agency and creates hazardous gases when applied. Treating those gases to mitigate toxicity could be done at the application site, but it would add significant cost to the process.
Older exhaust manifolds are usually cast-iron painted to resist corrosion. But using cast iron in the new drive would mean a larger, much-heavier design. Volvo Penta engineers wanted to use aluminum, so they needed a corrosion-protection scheme that would stand up to warm seawater.
The design team decided to go with an Alodine EC2 electroceramic coating from Henkel, Rocky Hill, Conn. It consists of an electro-deposited layer of titanium dioxide ceramic. The resulting surface reduces wear and surface friction and can be painted via electrocoating or liquid or powder paints, often without a primer.
In salt-spray exposure tests, unpainted EC2-coated aluminum showed no corrosion after 2,000 hr of exposure. Painted surfaces with EC2 went 7,000 hr without corrosion. Electroceramic-coated parts were also scratched and subjected to salt-water immersion and tidal testing. With EC2, scratched surfaces resisted corrosion damage creep, the deepening and widening of a damaged area.