Abstract
The individual influences of Fe, Si and Cu were examined, by adding 0.5, 1.0 and 2.0% to the Al-Zn-Mg alloys, containing Zn 7, Mg 1 (T-series), Zn 10, Mg 1(J-series) and Zn 1, Mg 5 (K-series), respectively. Age-hardening curves at room temperature and 150° for T & J-series and 200° for K-series were obtained (Rockwell B & H Hardness). The as-quench-hardness (H0) of each alloy was obtained by keeping the quenched alloys in a freezing mixture and measuring their hardnesses in the room below 0°. The tensile tests of the hardened alloys (aged at room-temperature and at 150° for T & J-series, 200° for K) were also carried out. The results were as follows :
Addition of Cu, up to 1% is almost harmless but the drawability will be decreased when it exceeds 1%. Si decreases the hardenability (ΔH) and reduces the strength. Fe increases the saturated-hardness (Hs) but reduces the hardenability, because the Al-Fe-Zn ternary compound “Y” is composed at the expense of Zn. Stress-corrosion-resistance will also be reduced by the addition of Fe. These harmful effects of Si and Fe may be reduced by increasing the Zn content, but no remarkable effect can be expected within the composition allowed for the commercial alloy (Zn+Mg<10). The Y-compound was detected both by the microscope and X-ray photograph, but composition and crystal structure of it has not yet been defined because of some difficulties in experimental technique.
