The substitution of steel materials with aluminium alloys can make a substantial contribution to the weight reduction of modern automobiles. Reducing the weight decreases fuel consumption and improves the environmental sustainability. The importance of secondary aluminium alloys for producing crash-relevant automobile components increases steadily, which is due to the distinct ecological as well as economical advantages of these materials. However, the comparatively high iron contents of secondary aluminium alloys affect the energy absorption capacity required to protect the passengers in the case of an accident. The suitability of three iron-containing Al-Si-Mg cast alloys for the production of crash-relevant automobile components is experimentally investigated in the present work. The investigations are performed for both the as-cast and the heat-treated alloy conditions. After composing the alloys in the melting furnace, U-shaped profiles are fabricated by squeeze-casting. Then a certain number of these profiles is heat-treated according to the SST- (Silicon Spheroidization Treatment) or to the T7-method, respectively. Characteristic mechanical parameters of the alloys are determined by tensile, plate bending and Charpy pendulum impact tests. The samples required for testing are taken from the cast and heat-treated U-profiles. Intermetallic phases are identified by incident light microscopy and scanning electron microscopy. The combined application of different analysis methods allows one to conclude how certain alloying elements and heat-treatment parameters influence the mechanical properties of the alloys. The investigations indicate that both of the T7-heat-treated Al-Si-Mg alloys with nominal contents of 7 wt.% silicon and 0.5 wt.% or 0.15 wt.% magnesium, respectively, exhibit very good impact energy and ductility values resulting in a high energy absorption capacity. Similar values shows the alloy with a nominal content of 7 wt.% silicon and 0.15 wt.% magnesium after the SST-heat-treatment. Highest ultimate tensile strengths and yield strengths, but only moderate impact energy and ductility values show both of the SST-heat-treated alloys with nominal contents of 0.5 wt.% magnesium and 7 wt.% or 10.5 wt.% silicon, respectively. Different intermetallic phases and precipitations which are substantially influenced by the alloy composition and the heat treatment are crucial for the mechanical properties and particularly for the energy absorption capacity of the alloys.