The first article concerns finding fine cracks in castings such as engine blocks. I can think of at least one situation where this info would have come in handy for me.
The second article is an experiment on the flow characteristics of silicon aluminum alloy.
A very telling experiment. For melting recycled aluminum, if you are casting thin sections and require good flow characteristics it only makes sense to choose similar recycled aluminum. Transmissions, small engine and compressor blocks, cooling fins from electrical equipment all have higher silicon content and will give better flow characteristics than chunky castings that did not require those flow characteristics to begin with.
If you like this kind of thing, keep an eye out for more posts from this information rich volume.