Eight metal elements affecting the properties of aluminum alloy (2)

 5. Metal elements: the influence of zinc

　　Al-Zn alloy system equilibrium phase diagram, the solubility of zinc in aluminum is 31.6% at 275 in the aluminum-rich section, and its solubility drops to 5.6% at 125. Zinc alone is added to aluminum, and the improvement of aluminum alloy strength is very limited under the premise of deformation, and there is stress corrosion cracking and tendency, thus limiting its application.

6. Metal elements: the influence of iron and silicon

Iron is added as alloying element in Al-Cu-Mg-Ni-Fe series wrought aluminum alloy, silicon in Al-Mg-Si series forged aluminum, Al-Si series welding rod and aluminum-silicon forged alloy. Among base aluminum alloys, silicon and iron are common impurity elements, which have a significant impact on the performance of the alloy. They mainly exist as FeCl3 and free silicon. When silicon is larger than iron, β-FeSiAl3 (or Fe2Si2Al9) phase is formed, and when iron is larger than silicon, α-Fe2SiAl8 (or Fe3Si2Al12) is formed. When the ratio of iron to silicon is not right, it will cause cracks in the casting, and if the iron content in the cast aluminum is too high, the casting will be brittle.

7. Metal elements: the influence of titanium and boron

　　Titanium is a commonly used additive element in aluminum alloys and is added in the form of Al-Ti or Al-Ti-B master alloys. Titanium and aluminum form the TiAl2 phase, which becomes the non-spontaneous core during crystallization, and plays a role in refining the forging structure and the weld structure. When the Al-Ti alloy produces a clad reaction, the critical content of titanium is about 0.15%. If boron is present, the deceleration is as small as 0.01%.

8. Metal elements: the influence of chromium and strontium

Chromium forms (CrFe)Al7 and (CrMn)Al12 intermetallic compounds in the aluminum plate, which hinders the nucleation and growth process of recrystallization, has a certain strengthening effect on the alloy, and can also improve the toughness of the alloy and reduce the susceptibility to stress corrosion cracking . However, the quenching sensitivity is increased at the venue to make the anodic oxide film yellow.