• T6-200°C/1h aging produces dense G.P. zones, yielding one order of magnitude lower steady-state creep rate than T6-275°C/8h with Al2Ca phases.
• The high stress exponent (~8.2) in T6-200°C/1h indicates power-law breakdown, with creep controlled by cross-slip between basal and prismatic dislocations.
• T6-275°C/8h exhibits mixed creep mechanism of dislocation cross-slip and climb, less effective in impeding dislocation motion.
• Dense G.P. zones are more effective than Al2Ca phases in blocking dislocation climb and glide, enhancing creep resistance.