Speaking of loose terminal screws. Is it bad code to loctite them?
Sometimes, the problem isn't that the terminal unscrews, but that the conductors flow. Thread locker won't help.
One of the big problems with aluminum wiring -- at least in the smaller gauges -- is that when the terminal heats up, the aluminum (which has a higher thermal coefficient of expansion than copper) tries to expand, but is constrained by the head of the screw and the backing plate. This increased pressure on the aluminum causes deformation -- it tends to squish or flow out the unconstrained side (aluminum is also usually more malleable than copper). Then, when the terminal cools, the deformed aluminum shrinks, and the connection becomes slightly looser than before. Because the connection is looser, the resistance can increase, causing it to heat up more next time. And the more it heats up, the more it deforms and the connection gets looser and looser.
With copper, the problem isn't nearly so onerous, because copper is a little more elastic (resilient) than aluminum, so after the terminal heats and cools, the copper tends to return to its original shape, maintaining the tightness of the connection. Copper oxide is also more conductive than aluminum oxide.
With stranded wire -- even if it's copper -- there can be a problem with these screw terminals in that handling of the cable can cause the strands to wiggle around in the terminal. That wiggling results in the structure of the strands deforming, just as happens with solid aluminum wire. Crimped connections generally constrain all the strands with no space for the strands to wiggle out, so they tend to be reliable.
Probably the best way to combat loose screw terminals in replacement cord ends is to make sure that the strain relief is securely fastened to the jacket of the cable, and to periodically check the terminations, as others here recommend.
