Comprehensive guide to nickel-based alloys: Monel 401 (UNS N04401)
Monel 401 (also known as "Alloy 401"), designated UNS N04401, is a copper-nickel alloy designed for special electrical and electronic applications. It has a very low temperature coefficient of resistance and a mid-range resistivity. Alloy 401 can be easily welded by gas tungsten arc welding (GTAW) or resistance welding. Monel 401 is usually supplied in wire form and is mainly used for wire-wound precision resistors and bimetal contacts. Monel 401 is a ductile copper-nickel alloy with extremely low resistivity and resistance to a wide range of corrosive conditions. Like commercially pure nickel, Monel 401 is less strong in the annealed condition and can only be cold worked to a maximum of 120 KSI.
Machinability of Monel 401
Traditional machining techniques used for ferrous alloys can be used for this alloy.
Welding Monel 401
Alloy 401 is easily automatically welded into thin sheets. Gas tungsten arc welding is a common welding method and welding process. Resistance welding is a satisfactory method for this alloy. Common welding methods are suitable for this alloy. Matching alloy filler metal should be used. If a matching alloy is not available, the closest alloy rich in the basic chemical composition (Ni, Co, Cr, Mo) should be used. All weld beads should be slightly convex. There is no need to use preheating. Surfaces to be welded must be clean and free of oil, paint or crayon marks. The cleaning area should extend at least 2 inches beyond both sides of the welded joint.
Gas tungsten arc welding: It is recommended to use DC positive electrode (negative electrode). Keep the arc length as short as possible and be careful to keep the hot end of the filler metal within the protective atmosphere at all times. Shielded Metal Arc Welding: Electrodes should be stored dry and if damp, the electrode should be baked at 600 F for one hour to ensure dryness. Current settings range from 0.062 amps for 50-inch-thick materials to 2 amps for 190/1-inch and thicker materials. It is best to slightly braid the electrode as this alloy weld metal does not spread easily. Use a wire brush (hand or electric) to clean the slag. It is important to completely remove all slag before successive passes and after the final weld.
Gas Metal Arc Welding: Reverse polarity DC should be used, with best results obtained when the welding gun is 90 degrees to the joint. For short-circuit transfer GMAW, typical voltage is 19-25, current is 100-175 amps, and wire feed speed is 225-400 inches per minute. For spray transfer GMAW, the voltage is 26 to 33, the current is 200-350 amps, and the wire feed speed is 200-500 inches per minute, depending on the filler wire diameter.
Submerged arc welding: The same matching filler metal as for GMAW should be used. DC current with reverse or forward polarity can be used. Projection welds are preferred.
