Nope, the pot metal used in the infamous "Saturday Night Specials" of old was extremely brittle due to the fact that it was essentially scrap metal, and as such had tons of impurities, was extremely inconsistent in terms of composition, and had absolutely no QC.

ZAMAK is an industry standard alloy consisting of exact percentages of Zinc, Aluminum, Magnesium, and Copper. The only way it can fail is if the manufacturer didn't use enough of it, but thankfully, firearms manufacturers who use ZAMAK these days don't want to be sued into bankruptcy or become synonymous with producing dangerously unreliable firearms like Raven/Phoenix/Bryco/Jennings/etc, so they build them properly.
If any proof is necessary to convince you of the structural integrity of ZAMAK, then have a look at this...


It's only 12 minutes long, but if that's too long for you, then skip to the end when he actually shoots the Hi-Point's slide with another pistol, and not only does it withstand the force, but continues to function reliably afterwards, not bad for a $150 pistol made of ZAMAK.