| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1994: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1993: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Three different Al-4.5%Zn-1%Mg alloys ; alloy No.1 with no addition of chromium, titanium and zirconium, alloy No.2 with 0.2%Cr and 0.06%Ti and alloy No.3 with 0.2%Cr, 0.06%Ti and 0.1%Zr were prepared. Ingots obtained were homogenized at 470ﾟC for 8 hours and then hot-rolled under different conditions to give different microstructures. Alloy No.1 showed aspect ratio of crystal grains about 4, alloy No.2 showed aspect ratio of about 9, and alloy No.3 aspect ratio of above 160. The hot plates were solution-treated at 450ﾟC for2 hours, water-quenched and aged at 120ﾟC to peak-age conditions. The rod shape of tensile specimens and specimens for 3 point bend test were cut from the aged final plates. Tensile test was carried out at the various temperatures between 7 to 293K.3 point bend test was carried out at 4.2,20-23,77.4 and 293K.
Proof stress, tensile strength, uniform elongation, work done for tensile fracture increase with decreasing temperature to about 20K and decrease gradually with temperature for the three alloys. Data of ductility and toughness at cryogenic temperatures of Al-Zn-Mg alloys are novel and very important. Temperature dependence of fracture toughness K_Q and R_<Sb> correspond to the uniform elongation and work done for tensile fracture. High ductility and toughness are obtained in order of alloy No.3, No.1 and No.2. Alloy No.3 with the typical lamellar structure, aspect ratio above 160, showed the highest ductility and toughness and the lowest strength. Alloy No.1 with aspect ratio of about 4 showed higher ductility and toughness than alloy No.2 with aspect ratio of about 9. Thus, correspondence with ductility or toughness and the degree of lamellar structure is not so strong.
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