An investigation has been made on the effect of additions of up to 0.7 wt% Cu and between 0.33 and 0.56 wt% Si on the extrusion performance of a series of alloys based on the AA6111 composition (0.69 wt% Si-0.70 wt%Mg-0.70wt%Cu). It was found that additions of both Cu and Si to the basic alloy decreased the extrudability: the extrusion speed decreased and the breakthrough force increased. Extrusion limit diagrams were constructed, at the specific pressure of 600 and 700 MPa at temperatures between 400 and 500 degreesC. In samples extruded at the limit speed, press quenched (cold water) and aged at 170 degreesC for 8 hours, the addition of Cu to the basic alloy significantly increased the UTS. However, the increase of Si additions did not have a significant effect on the tensile properties of the alloys following press quenching and ageing. When the extruded alloys were solution treated at 565 degreesC for 30 minutes, water quenched and aged an increase in Si concentration did increase the tensile properties.