Is this an aluminum screw dislocation?
No, what is occurring is the mercury is forming a eutectic liquid (also called an amalgam) with the aluminum. Aluminum is quite reactive with air/water, but typically aluminum can form an oxide coating that protects it from a complete reaction with air/water (passivation). When the mercury is added and the surface of the aluminum is damaged (by the drill) the two are free to mix per the phase diagram below now the aluminum in the liquid may react with the air/water, but now on the liquid the oxide formed is easily disrupted, and thus ineffective in protecting the aluminum from oxidation. This allows more aluminum to oxidize and the mercury to dissolve more aluminum as aluminum is depleted from the liquid. This creates a steady state condition where aluminum is continually dissolved and oxidized until the aluminum is completely consumed.



A screw dislocation is a microscopic feature only visible with atomic scale imaging such as with a tunneling electron microscope (TEM).