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Aging Strengthening Method of Aluminum Alloy

Another strengthening effect of alloying elements on aluminum is realized by heat treatment. However, aluminum has no isomeric transformation, so its heat treatment phase transformation is different from that of steel. The heat treatment strengthening of aluminum alloy is mainly due to the large solid solubility of alloy elements in aluminum alloy, which decreases sharply with the decrease of temperature. Therefore, after aluminum alloy is heated to a certain temperature and quenched, supersaturated aluminum based solid solution can be obtained. When the supersaturated aluminum based solid solution is placed at room temperature or heated to a certain temperature, its strength and hardness increase with time, but its plasticity and toughness decrease. This process is called aging. Aging at room temperature is called natural aging, and aging under heating conditions is called artificial aging. The phenomenon of increasing the strength and hardness of aluminum alloy during aging is called aging strengthening or aging hardening. The strengthening effect depends on the age hardening phase produced in the aging process.

The aging strengthening process of aluminum copper alloy is divided into the following four stages:

The First Stage

In supersaturation α ,The segregation of copper atoms occurs on a crystal surface of the solid solution, forming a copper atom enrichment region (GP [Ⅰ] region) α The solid solution produces serious lattice distortion, the dislocation movement is hindered, and the strength of the alloy is improved.

The Second Stage

With the extension of time, the GP [Ⅰ] region further expands and becomes orderly, forming an orderly copper rich region, called GP [Ⅱ] region, whose composition is close to CuAl2（ θ Phase), becoming an intermediate state, commonly used θ″ express. θ″ The precipitation is further aggravated α The lattice distortion of the phase further improves the strength of the alloy.

The Third Stage

With the further development of aging process, copper atoms continue to segregate in GP [Ⅱ] region. When the ratio of copper to aluminum atoms is 1:2, a transition phase maintaining a coherent relationship with the parent phase is formed θ′。θ′ At the beginning of the phase, the lattice distortion of the parent phase reaches the maximum and the alloy strength reaches the peak.

The Fourth Stage

Late aging, transitional phase θ′ It completely falls off from the aluminum based solid solution to form an independent stable phase CuAl2 with obvious phase interface with the matrix, which is called θ Phase. At this point, θ The coherent relationship between phase and matrix is completely destroyed, and the coherent distortion also disappears θ With the aggregation and growth of phase particles, the alloy softens obviously, and the strength and hardness decrease.