Monel K500® _ UNS N05500 >Monel K-500® is a nickel-copper alloy with the same corrosion resistance and characteristics as the Monel 400®. The Monel K-500® has a greater strength and hardness then the 400, as a result of added aluminum and titanium. In age-hardened condition, it has greater tendency toward stress- corrosion cracking in some environments.