With a cheap, non ruggedised laptop, I would NOT recommend using a file on it. One thing that might work is using a 400 grit or finer grit sanding block as gently as possible to ease the sharp edges.
At the same time though, be warned however that depending on the gauge of aluminum used, you may very well wind up sanding a hole through the aluminum. Also be warned that the aluminum most likely also has a hard anodised finish, which protects it from galvanic corrosion. --If you sand it, you are also removing the protective coating which will accellerate galvanic corrosion caused by sweat, ocean air/marine environment, or any form of salt/acidic exposure.
FWIW, I use a Panasonic Toughbook CF-T8. This is one of Panasonic's 'business rugged' ultra portable notebooks. The case construction is of cast/machined magnalloy for the bottom of the clamshell, and cast/machined magnalloy and stamped aluminum for the screen assembly. During the time that I have used it, it has experieced some paint lifting from some slight galvanic corrosion that it recieved from being stored in a non-waterproof bag that sat on the floorboards of a work truck that was wet with road salt infused snowmelt during the winter of 2013/14.
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