Hi All,
Just keep in mind that helium additions to argon of over 10% change the arc characteristics. With increasing helium content, the arc voltage and spatter will increase as well. As backpurge said, the addition of helium produces a hotter arc which is sometimes necessary due to aluminum’s high thermal conductivity. It also produces a wider weld fusion shape. As John said, cleaning should be done just prior to welding to prevent the formation of oxides. The base metal surface must be free of grease, oil, paint, dirt, etc. A clean surface will provide a smoother, stronger joint. Brush the plate surface & edges with a stainless steel wire brush to remove burrs & oxides. Gloves should be worn to prevent hand oil or dirt from getting on the joining surface.