In order to meet the increasingly demanding requirements for aluminum alloys, a higher strength hard aluminum alloy has been developed, which is the strongest of the deformed aluminum alloys. It is characterized by the addition of elements such as zinc and chromium on the basis of general aluminum alloys. And its trace elements, using the matching effect of various elements to strengthen, has obtained higher strength, has been made into high-strength aluminum alloy 7000 series super-hard aluminum alloy, typical representative 7075;
The strength and fracture toughness of the super-hard aluminum alloy are uniform due to the hard aluminum alloy, but the fatigue resistance is poor, and the heat resistance is also lower than that of the hard aluminum. Under appropriate heat treatment conditions, 7005, 7039 can get medium strength of 300~450Mpa.
Both chromium and manganese are trace additives commonly used in super-hard aluminum alloys. These elements strongly increase the recrystallization temperature of the alloy and hinder the recrystallization process. In the past, trace elements were used to improve the stress corrosion resistance. The addition of TI and ZR not only refines the grain, but also improves the weldability. The weld is softened during the welding process. It can also be recovered by natural aging. It is suitable for heat treatment after welding and welding components. It is also called medium-strength or high-strength weldable aluminum alloy.
The corrosion resistance of super-hard aluminum alloy is stress corrosion cracking and the sensibility is large, and there is also a tendency of corrosion and corrosion between crystals. However, the inductiveness of intergranular corrosion is inferior to that of aluminum-copper-magnesium alloy, and the corrosion tendency is also better than that of LV-MN-MG. The alloy is small, the lv-zn-mg-cu alloy and the other corrosion characteristic is that during the processing, mainly the tubes, rods and profiles are prone to pitting corrosion during the vertical quenching of air, and the corrosion characteristic is “white ban black”. core".
The corrosion resistance of super-hard aluminum alloy is worse than that of hard aluminum. The stress corrosion cracking is very sensitive, especially in the case of quenching. Therefore, the aluminum alloy has not been applied in industry for a long time, but it has only been developed in recent years. try out. The alloy grade is still very small. The stress corrosion of AL-ZN-MG-CU alloy depends on the content of zn and mg. Whether it is increasing the zn content or increasing the mg content, the effect of zn is stronger than the effect of mg. When zn+mg=8.5% and zn/mg=2.7-3.0, the stress corrosion resistance is the best.
Super-hard aluminum alloy is also protected by a coating method, but it is not covered with pure aluminum, but is coated with AL-ZN alloy because the point of tea between pure aluminum and super-hard aluminum alloy is very large and cannot be protected. effect.
Super-hard aluminum is mainly used in the superstructure of ships on aluminum alloy ships.