When sourcing aluminium frames, the alloy grade is the most critical factor; 6063-T5 is standard for architectural windows and doors due to its excellent finish, while 6061-T6 is preferred for structural applications requiring higher strength. You must also specify the wall thickness, typically ranging from 1.2mm to 3.0mm, to ensure structural integrity. Additionally, evaluate the surface treatment options such as anodizing (minimum 10-15 microns) for corrosion resistance, powder coating for color variety, or electrophoresis for a high-gloss, durable finish.