From aluminum intensive processing

China’s aluminum alloy research and development work is about 50 years later than the traditional industrial powers, the current independent research and development of aluminum alloy brands, materials are also very limited. Since 2000, the world Aluminum Association (AA association) registered the main aluminum alloy brand and its membership statistics show that the new application of about 140 kinds of aluminum and aluminum alloy brand, the traditional industrial power (region) accounted for more than 90%, China less than 3%.

Substantial progress has been made in the development and production of the third and fourth generation aluminum alloys with high performance and large specifications and the new generation of aluminum alloys with high strength, high toughness, low density and low quenching sensitivity. Advances in 7XXX, 2XXX and al-li alloys are described below.

(1) 7XXX aluminum alloy

Based on the high strength characteristics of 7XXX series aluminum alloy, the synergistic action law and mechanism of composition, precipitation relative strength and toughness and hardenability are explored. As shown in Figure 2, the hardness and quenching sensitivity of Al-8Zn-XMg-1.6Cu alloy can be controlled by changing the magnesium content (1#-1.0%, 2#-1.4%, 3#-2.0%).

Relationships between Mg content, hardness and quenching sensitivity of Al-8Zn-xMg-1.6Cu alloy: (a) Hardness increasing with Mg content; (b) Quenching sensitivity increasing with Mg content

The grain structure, toughness, stress corrosion resistance and quenching sensitivity of high strength 7XXX aluminum alloy were improved by adjusting the contents and types of trace elements Cr, Mn, Ti, Zr and Sc in the alloy. For example, aluminum alloy with Zr as trace element (such as 7050, 7055, 7085, etc.) has better stress corrosion resistance than aluminum alloy with Cr and Mn as trace element (such as 7075, 7049, etc.). More importantly, zr-containing high-strength aluminum alloy has a low quenching sensitivity, so this kind of alloy can be widely used in large load bearing members. The results show that the dispersion particles containing Cr and Mn do not coincide with the matrix, so that the quenching equilibrium phase can precipitate preferentially at the phase interface between the particles and the matrix. However, the zr-containing dispersion particle (Al3Zr) has a coherent interface with the matrix, which greatly reduces the possibility of precipitation of equilibrium phase on the zr-containing dispersion particle interface during quenching. Some Al3Zr dispersion particles can also induce the precipitation of equilibrium phase during quenching, because the migration of grain boundary during recrystallization leads to coherent and incoherent transition of Al3Zr dispersion particles. As shown in Figure 3, the phase interface of incoherent Al3Zr dispersion particles induced the precipitation of the second phase, which increased the quenching sensitivity. So quenching sensitivity control can be transformed into dispersion particle type control or recrystallization fraction control.

The recrystallization of Al3Zr dispersive particle takes place common-incoherent transition and induces the precipitation of the second phase

In conclusion, the uniformity and stability of high-strength aluminum alloy materials require strict control of material preparation process parameters and strengthening process management, and the correlation law of alloy composition, process, microstructure and properties plays a decisive role, involving the complex formation mechanism and function of macro/fine/micro multi-scale microstructure. This is also the modern aviation aluminum alloy material level is considered to represent the essence of aluminum alloy material strength of science and technology.