TIG welding magnesium question

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A few weeks ago I needed to make a couple of repairs to a magnesium oil pan that was ground through while adding clearance for main studs.  I prepped the metal as if I was welding aluminum, SS wire brush to remove the blackish layer (an oxide?) then an acetone wipe.  The filler rod was wiped with scotch brite and then an acetone wipe till the rag was clean after a wipe then snipped the leading tip off.One steel block was clamped to the inside of the pan and one against the pan rail to create a pocket of shielding gas on both sides of the weld and pre flow was to 4 sec.  The steel blocks also helped to reduce warping.The machine was a Thermal Arc 185TSW, 75%helium 25%Ar, with a 1/16 1.5% lanthanated tungsten.  The repair came out good.Here's the question.  When I started out I figured the casting would be dirty and require a high DCEP setting to clean the puddle, at 30% it still looked dirty so I turned it up to 35% then 40% but the arc got louder, and began to qiver (I think too much DCEP for the 1/16 tungsten)  and the puddle was actually getting dirtier.  Then I turned the machine down to 15% DCEP and the puddle was cleaner and then even cleaner at the lowest setting of 10%.  Is this normal for TIG welding magnesium?Can any part of this be due to the helium in the shielding gas breaking up the oxide layer as if it was DC Heliarc welding?This was my first time working with magnesium and I was told to expect it to weld like a dirty aluminum casting.~Alex
Reply:Magnesium just fumes out like that. It leaves smut all around the weld. All you can do is keep cleaning it.You did good.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Originally Posted by shovelonMagnesium just fumes out like that. It leaves smut all around the weld. All you can do is keep cleaning it.You did good.
Reply:Just curious as I have a job coming up. Was this pure magnesium or a magnesium-aluminum alloy? What filler did you use?
Reply:What rod do you use for magnesium? And on AC right?Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Originally Posted by GambleWhat rod do you use for magnesium? And on AC right?
Reply:Originally Posted by montgoc3Not sure about him, but in the past I've used AZ92A rod and on AC.  I paid around $150/lb for the rod.  Not cheap.
Reply:This was welded on AC, I'm not sure if it was pure Mg or a mix and I'll take a look at the filler rod tomorrow.
Reply:Some interesting videos on welding magnesium if they can help you: "Hey I didn't come to look and learn, I came to turn and burn.... If I can't light up, I'm gonna light out!"-JodyIdealarc 250 "Fatman"MM 252MM 211 "Little boy" Victor Torches
Reply:Originally Posted by ANVILSome interesting videos on welding magnesium if they can help you: