LM20 alloy is rather difficult to machine because of the rapid tool wear caused by the high silicon content and because of its tendency to drag. The small amount of copper present results however in a slight superiority in this latter respect over LM6.
Carbide-tipped tools with large rake angles and relatively low cutting speeds give comparatively good results. A cutting lubricant and coolant should be employed.
LM20 exhibits high resistance to corrosion under both ordinary atmospheric and marine conditions being only slightly inferior in respect to LM6; resistance may be considerably increased by anodic treatment.
LM20 can be anodised by any of the common processes, the resulting protective film ranging in colour from grey to dark brown. The surfaces of die castings, however, are not generally suitable for decorative anodising.
LM20 is suitable for marine castings, water jackets, meter cases, domestic and office equipment, street lighting and other castings subjected to atmospheric exposure.
In general LM20 alloy is preferred to the more common die casting alloys LM2 and 24 only when the castings are used in aggressive media requiring the rather higher corrosion resistance of the copper-free alloy. Where the very highest resistance to chemical attack is required LM6 alloy may be superior to LM20.