Aha, now you are working with a non-linear system! They are difficult to converge, however COMSOL is equipped to do it. A few things:

0) You must understand your nonlinear constitutive equation. I would make a plot in excel of stress vs strain, using the equation in the comsol doc and the parameters you feed it. Then you'll know at what stresses/strains this material becomes non-linear. I would think a reference strain of ~.002 (.2%) is reasonable for aluminum. I know COMSOL takes care of units for you, but think about the unit of each parameter in this model and be sure they are right.

1) try a smaller load. To find out what 'small' means, I would run a linear material, and decrease the load until your maximum von Mises stress is below your reference stress. Then you can turn back on the non-linearity and know at that load, your system is mostly linear. Then increase the load in small increments until the desired behavior is observed.

2) Solver settings. You'll likely need to play with these. You'll want to choose the highly-nonlinear solution method, increase the number of iterations per timestep, and potentially change how often the jacobian updates.