The role of trace elements in die castings

- Jul 10, 2017-

1. Titanium and boron

Titanium is commonly used in aluminum alloy to add elements to Al-Ti or Al-Ti-B center alloy way to participate. Titanium and aluminum constitute TiAl2 phase, become the crystallization of the non-conscious center, from the refinement of forging tissue and weld tissue effect. Al-Ti alloy package reaction occurs, the critical content of titanium is about 0.15%, if the presence of boron is reduced to 0.01%.


2.Iron and silicon

Iron in the Al-Cu-Mg-Ni-Fe system of forged aluminum alloy, silicon in the Al-Mg-Si series of aluminum and in the Al-Si electrode and aluminum silicon forging alloy, are added as alloying elements in the In its aluminum alloy, silicon and iron are the common impurity elements, which have a distinct effect on the alloy function. They are predominantly present as FeCl3 and free silicon. When the silicon is larger than iron, the β-FeSiAl3 (or Fe2Si2Al9) phase is formed, and when the iron is larger than the silicon, α-Fe2SiAl8 (or Fe3Si2Al12) is formed. When the proportion of iron and silicon is not enough, will cause cracks in the castings, cast aluminum iron content is too high will cause the casting brittle.



The addition of chromium in the aluminum alloy generally does not exceed 0.35%, and with the alloy in the transition elements to increase. Chromium is commonly added to Al-Mg-Si, Al-Mg-Zn, Al-Mg alloys. 600 ℃, chromium ablation in aluminum was 0.8%, at room temperature did not melt.


Chromium in the aluminum (CrFe) Al7 and (CrMn) Al12 and other intermetallic compounds, barrier recrystallization nucleation and growth process, the alloy has a certain strengthening effect, but also improve the toughness of the alloy and reduce the stress corrosion cracking sensitivity The But the venue to add quenching sensitivity, so that the anodic oxide film was yellow.



Strontium is the appearance of active elements, in the crystallization of strontium can change the behavior of intermetallic compounds. The metamorphic treatment with strontium can improve the plasticity of the alloy and the final product quality. Because strontium transformation is useful, the results and good reproducibility, in recent years in Al-Si forging alloy instead of the use of sodium. In the extruded aluminum alloy, 0.015% ~ 0.03% strontium was added to make the α-AlFeSi phase of the β-AlFeSi phase in the ingot, reducing the proportion of the ingot averaging 60% ~ 70%, improving the mechanical function and Plastic processing; improve the appearance of the finished product roughness. On the high-silicon (10% ~ 13%) deformation of aluminum alloy to participate in 0.02% ~ 0.07% strontium elements, the initial crystal can be reduced to a minimum limit, the mechanical function is also significantly improved, the tensile strength бb from 233MPa to 236MPa, Б0.2 from 204MPa to 210MPa, the extension rate of б5 from 9% to 12%. In the hypereutectic Al-Si alloy to participate in strontium, can reduce the size of the primary silicon particles, improve the plastic processing function, can be smooth hot rolling and cold rolling.


5. Zirconium elements

Zirconium is also a common additive for aluminum alloys. Ordinary in the aluminum alloy in the amount of 0.1% to 0.3%, zirconium and aluminum constitute ZrAl3 compounds, can be obstacles to the process of recrystallization, refinement of recrystallized grains. Zirconium can also refine the forged tissue, but smaller than the titanium results. In the presence of zirconium, the results of thinning of titanium and boron are reduced. In Al-Zn-Mg-Cu alloys, zirconium is used instead of chromium and manganese to refine the recrystallized structure because zirconium has little effect on quenching sensibility than chromium and manganese.