In this present paper friction stir welding of dissimilar heat treatable aluminium alloys 7020-T651 and 6060-T6 has been studied. An experimental analysis is presented based on results obtained from temperatures and efforts measurements in a range of advance speed from 300 to 1100 mm min(-1) and rotation speed from 1000 to 2000 rev min(-1). Dissimilar welding does not seem to induce a hotter side but efforts are very sensitive to process parameters. The material mixing of dissimilar configurations has been investigated by means of macro and microstructural observations and has revealed the complex mechanisms of material flow into the nugget. The as-welded mechanical behaviour has been characterized using quasi static tensile tests. The cross-weld microhardness has also been studied for various operating parameters. Computed maps correlated the microstructural features helping us establish weak zones. All these characterizations make it possible to determine a large window of industrial parameters capable of welding properly two 5 mm sheets of AA7020-T651 and AA6060-T6 with good mechanical properties. (C) 2016 Elsevier B.V. All rights reserved.