Method of continuously heat-treating 7000-series aluminium alloy sheet material

The invention relates to a method for continuously solution heat-treating aluminium alloy sheet by continuously moving heat-treatable 7000-series aluminium alloy sheet through a continuous heat-treatment furnace arranged to heat the moving aluminium sheet to a set soaking temperature (T SET ) in the temperature range of 370°C to 560°C, the continuous heat-treatment furnace has an entry section and an exit section, the moving aluminium sheet moves substantially horizontally through the continuous heat-treatment furnace, and wherein the moving aluminium sheet is rapidly cooled on leaving the exit section, and wherein before or near the entry section of the continuous heat-treatment furnace the moving aluminium sheet is pre-heated to a temperature of 5°C to 100°C below the T SET using an average heat-up rate as function of the sheet thickness of at least Y = -31.ln(X) + 50, wherein Y is the heat-up rate in °C/sec and X is the sheet thickness in mm.