 The typical value for thermal conductivity for 6061-T6 at is around 152 W/m K.
A material data sheet  defines the fatigue limit under cyclic load as for 500,000,000 completely reversed cycles using a standard RR Moore test machine and specimen.Note that aluminum does not exhibit a well defined "knee" on its S-n graph, so there is some debate as to how many cycles equates to "infinite life".Also note the actual value of fatigue limit for an application can be dramatically affected by the conventional de-rating factors of loading, gradient, and surface finish.