This is actually the first time ive heard of mill scale! I shall be grinding the areas where the weld eill be from now on thanks'
Oh yea, always clean/shine where the welds will go. You can run the welder a bit hotter and that will burn the stuff off and still give you a good weld, but it's best if there's nothing to burn off to begin with. Few questions:
1) where are your recovery points? The receiver can obviously be used as one with a shackle on a drawbar, however what if you have the winch in there already and you're doing a double-line pull so you can get down in your rope layers (less rope on drum = more pulling power from winch, and the block will double it on top of that)? If you ever need to hook the winch line to yourself, where do you hook up? Just something to think about...
2) how big is your cross-tubing, that would be the two tubes that hold your receiver? Looks like a 1x1 or 1.25 x 1.25 - in a hard pull you're very likely to bend those. A 1x2 laid on its wider side would have worked out better, you can achieve that easily be adding another cross-tube behind the upper one, this one longer and running from one end to the other behind both the upper tube and the flat plates that hold your bumper to the frame.
3) the bolts holding your bumper in place, are they grade-8 and did you weld them in place and if you did is it a full-perimeter weld or just a few tacks? Grade 5 you can weld all day long no problem, with grade-8 there have been concerns about the heat hardening it too much thus making it brittle. My work around that when it's needed is using a flange-head grade-8 bolt, then do just 3 "heavy" tacks 120 degrees (1/3 turn) apart - if both the bolt and the steel it holds are shined up well that's enough for good penetration to hold the thing still while fighting a potential rusted-on nut in the future, but still not hot enough to mess up with the bolt metalurgy itself, and furthermore the flanged head provides better clamp load spread and thus much less likely to tear the metal if bolt is put in heavy tension.
Not nit-picking your work, just trying to provide some constructive criticism. And now here's another suggestion - from the bottom of your front plate, weld another one down (maybe 2-3" tall), and angle it back - the idea is to hide that factory crossmember under the bumper as that thing will get caught on everything. This additional plate will reinforce your bumper, hide the crossmember, and with proper gusseting and tabbing will give you two more attachments points for the bumper to frame (I see there is a hole under the factory crossmember under each frame rail, looks like at leas 7/16" in size, use those!)