The toughness and ductility of AL-6XN® alloy provides for relative ease of fabrication in the shop or field environments.
AL-6XN® alloy provides better formability and weldability compared to high alloy ferritic or duplex stainless steels that demonstrate comparable corrosion resistance. AL-6XN alloy products can be welded in the field using similar weld procedures as other austenitic stainless steels.
AL-6XN alloy is easily welded using similar weld techniques and equipment as 316L stainless steel, including travel speed (IPM) and weld current. Use weld insert rings for additional alloying when orbital or manual welding in the field. The insert ring alloy must have higher molybdenum content than the AL-6XN alloy to compensate for alloy dilution on cooling. Typically Hastelloy® C-22® (13% Mo) is used, but if C-22 is not available, Alloy 625 (9% Mo) or Alloy C-276 (15% Mo) may be substituted. When using weld ring inserts, simply place the weld ring between the two sections to be welded and fusion weld as usual. The weld current must be increased slightly to compensate for the increased thickness of material contributed by the insert ring.
Use inert gas for both the weld cover and backing. Either helium or argon may be used, although argon is more commonly used. Never use filler wire in place of weld rings for sanitary tubing; welding techniques that apply filler wire to the weld face are not recommended, due to the possibility of insufficient alloying in the weld root.
Consumable weld rings made from Hastelloy® C‑22® (or another alloy containing more Molybdenum than AL‑6XN) are used to over-alloy each weld. This maintains the high corrosion resistance you expect from AL‑6XN.
AL-6XN weld appearance can be somewhat misleading when compared to hygienic welds in 316L stainless steel. A typical AL-6XN weld will have non-uniform freeze lines and slag islands in the weld bead. The slag islands are dull or blue-gray in color and adhere to the surface. Light and dark spots on both the inside and the outside of the weld are also common. The heat-affected zone can also have discoloration and is generally a little darker than typical 316L stainless steel welds.
Alloys that have more than 3% molybdenum typically require over alloying, because iron-nickle-chromium-molybdenum (Fe-Ni-Cr-Mo) alloys have a tendency to deplete molybdenum when welded. Typically, 2/3rd of the molybdenum content of the base metal gets reduced when welded.
316L has molybdenum in the 2-3% range, so 2/3rd of the molybdenum is reduced to approximately 2%, which is a minimal difference. With 316L and similar alloys with 3% or less molybdenum, corrosion resistance at the weld is minimally affected.
However, in superaustenitics, duplex alloys, or any other alloys that have more than 3% molybdenum, having a consumable weld insert will restore the corrosion resistance at the weld. Alloys such as AL-6XN®, 254SMO, 904L, 2507, 2205 have more than 3% molybdenum on average, so overalloying the weld, with at least 9% molybdenum, will keep the corrosion resistance at the weld.
Excellent results have been achieved in milling, turning, and drilling AL‑6XN alloy when appropriate tools are used. Since AL‑6XN alloy has a hardness of approximately 88 RB, selection of the proper tools and machine set-ups is the key to achieve adequate machinability. The high strength and work hardening capability of AL‑6XN alloy require more power to cut.
Our Alloy Specialists are happy to talk about whether AL-6XN is right for your application.
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