You seem to be wondering if the cations Potassium and Magnesium pose any additional concerns that Calcium and sodium do not.  In general, there are no chemical issues from a general corrosion point of view - steel, zinc, aluminum, stainless steel, cast iron etc, immersed in solutions of KCl, MgCl2 and CaCl2 will not corrode dramatically differently from a weight-loss point of view.  I see no major SCC issues either, except on hot surfaces - e.g. MgCl2 could cause SCC on stainless steel exhaust systems.  
However, this is a complex subject because the physical properties - solubility, hydroscopic behaviour, etc. are also important in defining how harmful deicing salts are because they affect the time of wetness arising from wet salt depostits on the car.  Most of the harm from road salt comes in the warmer months when residual deposits of salt stay conductive and corrosive because of the moisture they absorb and hold on the surface.

Much work has been done on automotive corrosion by salts(see R. Baboian's work, amongst others).

GMED

Food for thought... the "body structure" in NOT the only section that has potential for being affected by de-icing agents.

Aircraft are particullarly vulnerable to deicing materials in/on the following:
a.  electrical connectors [not fully sealed].
b.  exposed sections of landing gear shock-struts and brake assemblies.
c.  engine inlet and engine parts/sensors [high volume air intakes pull gobs of air/contaminates thru the engine and accessories].
d.  mating parts with unsealed areas that trap fluids and dust particles [abrasion].
e.  moisture/fluid puddling due to indaequate drainage... or blocked drains...etc.
f.  fluid/air vents that trap/ingest fluids in reverse[drain-pipes, oil vent lines, etc] due to high pressure spray or rapid changes in air pressure [forced and cappillary].
g.  contamination of sealed bearings/parts due to high pressure tire-spray fluid/particle spray intrusion [wheel, door, linkages, etc].
h.  and tire traction can be significantly altered.

Regards, Wil Taylor