increase at 150 u00b0 c peaking at about 225 u00b0 c for the first time with a microhardness of 287 u00b1 6 mpa it then decreases at higher temperatures but increases again at 375 u00b0 c peaking at about 475 u00b0 c for the second time with a microhardness of 451 u00b1 17 mpa the microhardness continuously decreases beyond an aging temperature of 475 u00b0 c al 0 1 zr 0 02 sn behaves similarly to the al 0 1 zr 0 01 sn alloy except that its first microhardness peak is at a lower temperature of 200 u00b0 c with a higher value of 357 u00b1 9 mpa and its second microhardness peak is at a lower temperature of 425 u00b0 c and a higher value of 493 u00b1 22 mpa it is noted that the first peak microhardness value of al 0 1 zr 0 02 sn occurring at 200 u00b0 c is the same as the peak microhardness value of al 0 1 zr alloy occurring at 500 u00b0 c it is also noted that the addition of 0 01 0 02 at of sn improves peak microhardness of al 0 1 zr from 367 to 451 and 493 mpa respectively while decreasing peak.