OK, lets look at some other aspects of this topic so you can continue practicing with a little more detailed look at MIG in aluminum.
Patterned MIG welds do accomplish several welding goals that are desirable. They are wider, without being proportionally thicker so the root face is 'bigger' but the weld deposit is not double that of a drag weld. That is a gain.
Patterned or whipped welds, usually use a transition between short arc and spray to increase wetting and then deposit a pure, porosity free, 'top layer' in the short arc mode, and last they allow a higher wattage weld to be applied without increasing the travel speed of the weld to 'machine' or robotic speeds.
But.. they are not the only game in town. Drag welds or non-patterned welds work fine and they need to be mentioned.
if you're familiar with welding with a coated electrode or 'stick' welding then you've probably welded a fillet between two 90deg pieces by just following the natural V formed between the two pieces? That is a fillet but if there is no pattern to the weld bead, so that weld could be performed by just 'dragging' the electrode. The term -drag weld- is used for a bead formed by moving uniformly along the weld area, even if you 'lead' the weld as in aluminum MIG. I'm not being intentionally inconsistent as these are terms widely used, so please let me know if this is (too) confusing?
Leading is to lean the cup to the right while welding toward the left or... leaning the cup to the left while welding to the right. Dragging a weld with a MIG gun would be to lean the gas cup to the right and weld to the right. [Just to get some terms clear, in case I use them in a confusing manner.]
this bead is a drag bead even if I put it down leading the weld from right to left (I'm a right handed welder) and then back stepped one puddle to 'crater out'. [More on crater/cratering out/weld ending coming]
This is just a close up view of the previous image but it contains info we can use. The clean zone looks inadequate but the last puddle is 'clean'? What's up with that? Well the weld was done with a constant lead and at a higher rate of travel than a 'stepped' or patterned weld so the gas cleans as you weld but the evidence or clean zones or white tracks are not as evident. What we do see is a toe and top fusion that is relatively even, not built up and the arc patterns are reasonably round and uniform inside the puddle.
All this indicates that we're approaching a decent balance of wire feed speed, wattage of weld power, travel, angle of the torch to work and gas coverage that ends in a reasonable bead profile.
wire brushing that same weld shows the fusion at toe and top is not a perfect as we could get. At the top there are tiny droplets of aluminum that were 'splashed' on to the parent metal showing that the wire speed was just tiny bit to slow, so the arc was more spray mode and there were some droplets that were 'stray' and they show along the boundary of this weld.
This is not a bad weld, I'm just trying to guide the reader to the better MIG bead. The arc contours are round, and that is a good indication of balance. However, the top of weld boundary area does show I could have added just a bit more wire speed to shorten the arc length , by a very small amount, to reduce this splash and thereby increasing the quality of my bead.
Drag or 'stringer' bead welds are very important skill to master in building welded aluminum boats. They are applicable to welds that do not lend themselves to patterned or wider, somewhat slower travel speed, welds. They are very useful to avoid distortion in some internal welds and are difficult to master since the amount of practice plate and argon required is high- (read expensive).
I wanted to make sure we don't ignore this important MIG bead in our discussion. I do realize it takes a bit more effort to learn this bead at the speeds implied by 0.045" wire if you weld on 0.125" or thinner material. Therefore, I would suggest this welding technique be used with 0.035" wire for 0.160" or thinner material OR
... 0.190" thick material or thicker parent material with 0.045" wire.
What the combination of wire diameter and parent metal thickness does, as given above, is to confine the welder to a set of more nearly matched wattage and rate of deposition that are easier to put down. You can, use 3/64" wire on thinner material but the movement is very high to create a drag that is proportional to the parent metal. [I would say that speed would come with the second 1000 hours of welding.]
Next let's look at the beads on the scraps prepared above.