Q: Is AL6XN a steel or nickel alloy? Trying to figure out if it would perform as well as Monel in seawater.
A: To answer your first question, AL6XN bolts are actually both a nickel and a steel alloy. AL6XN is often described as a high nickel content stainless alloy. Though AL6XN bolts are prodominently iron based with >40% iron, it also contains a large percentage (24%) of nickel and performs like a nickel alloy, meaning it offers high temperature and high strength corrosion resistance. AL6XN.
In comparing AL6XN to Monel 400 they are fairly similar with the same usable temperature limit of 1000°F and comparable yield strength (though AL6XN has a slight advantage of 53ksi to Monel’s 45ksi). Both perform excellent in seawater, yet Monel can show some pitting in stagnant seawater, where AL6XN Molybdenum content actually helps prevent pitting and crevice corrosion in seawater. If your application is not prone to stagnant water and you don’t need the added strength I would actually suggest Monel 400 bolts as they would be a more economic fastener.