Research status of the influence of hot processing on the micro-structure and properties of aluminum alloys

Research status of the influence of hot processing on the microstructure and properties of aluminum alloys.

Aluminum alloy,as one of the abundant metals in the Earths crust,second only to oxygen and silicon,has a wide and diverse range of applications.Aluminum alloys play an important role in aerospace,automotive lightweighting,3C electronics,sports equipment,machinery manufacturing,shipbuilding,and chemical industries.However,the low strength of pure aluminum,with a tensile strength of about 50 MPa,limits its application range.By adding other alloying elements to pure aluminum,aluminum alloy materials that meet various properties,functions,and applications can be manufactured.This article will focus on the influence of hot processing on the microstructure and properties of aluminum alloys,and summarize the current research statu

1.Overview of Classification and Hot Processing of Aluminum Alloys

Aluminum alloys are mainly divided into two categories based on the type,content,and properties of the added alloying elements:deformed aluminum alloys and cast aluminum alloys.Deformable aluminum alloys can be further divided into non-heat-treatable aluminum alloy and heat-treatable aluminum alloy.The preparation process of aluminum alloy usually includes steps such as melting and casting,homogenization heat treatment,hot working,cold working,heat treatment,and product performance testing.

Hot processing is one of the important processes in the preparation of aluminum alloy products,mainly including hot extrusion,hot rolling,hot forging,etc.Hot processing can effectively change the as cast micro-structure of aluminum alloys and improve the overall performance of the material.The common hot processing methods for aluminum alloys include hot extrusion,hot rolling,hot forging,hot top forging,liquid forging,semi-solid forming,continuous casting and rolling,continuous casting and extrusion,etc.

2.The Effect of Hot Processing on the Micro-structure of Aluminum Alloy

2.1The Effect of Heat Processing Deformation Temperature on Alloy Micro-structure

During hot processing,the deformation temperature has the greatest impact on the mechanical properties of the material.The deformation temperature directly affects the deformation microstructure,dislocation substructure,second phase precipitation rate,precipitate size and shape,and subsequent transformation.As the deformation temperature increases,the dislocation density gradually increases,and the interaction between dislocations and dislocations,as well as between dislocations and the second phase,confines dislocations to a certain region,forming a cellular structure.

When the deformation temperature is high,the mobility of the atom is enhanced,and the dislocation can cause the same dislocation annihilation,the same dislocation reorganization,and the multilateral occurrence by cross-sliding and climbing.This process reduces the energy of the deformed grain,and the dynamic softening phenomenon occurs,and the deformation gradually changes from the processing hardening stage to the steady state stage.When the deformation temperature is low,there is no sufficient driving force for dynamic re-crystallization,the alloy mainly occurs a certain degree of dynamic recovery,and the micro-structure shows a typical amorphous structure.

2.2Refining effect of hot working deformation on alloy structure

The hot processing deformation can effectively change the casting organization of aluminum and aluminum alloy.First,the deformation of thermal processing breaks the thick columnar grains in the cast tissue,and after repeated deformation,the tissue of the alloy becomes more uniform and small is-axial grains.At the same time,it can also heal some micro-cracks inside the alloy tissue.Second,under the action of external force,it can promote the bubble welding,hole compaction,compaction of loose compaction,and the alloy material into a more compact tissue structure.Third,due to the enhanced thermal motion ability of high temperature atoms,under the action of compressive stress,with the help of free diffusion of atoms,the degree of microscopic segregation of alloy can be reduced,and the uniformity of the chemical composition of alloy ingot can be improved.

3.Effect of hot processing on aluminum alloy properties

3.1.Rheological stress behavior

Rheological stress is an important mechanical parameter in the thermal processing process.The study shows that the rheological stress of aluminum alloy increases to the peak with the increase of stress variable,and then decreases to different degrees with the increase of stress variable.The magnitude of the rheological stress depends on the deformation temperature and the strain rate,which decreases with the deformation temperature and increases with the strain rate.

For example,the thermal compression experiment of 2024 aluminum alloy on Gleeble1500D with the compression parameter of 300-450℃,0.01-10s-¹,found that the rheological stress behavior of 2024 aluminum alloy conforms to the hyperbolic sinusoidal form of the Zener-Hollonmon function,with its thermal activation energy Q of 367.37kJ/mol.

3.2.Micro-organizational evolution

In the process of thermal processing,the micro organization of aluminum alloy will get changed significantly.As the deformation temperature increases,the softening mechanism in the material changes from dynamic regeneration to dynamic re-crystallization.As the strain rate increases,the degree of alloy dynamic recovery or dynamic re-crystallization decreases.

Through OM,EBSD and other experimental means,the evolution law of aluminum alloy tissue can be observed.For example,the optimal processing area of the 2024 aluminum alloy at the stress variable of 0.6 is 370-440℃,0.005-0.01s⁻¹.Under these conditions,the micro-organization of the alloy showed the best dynamic re-crystallization effect.

3.3.Mechanical properties

Thermal processing has a significant influence on the mechanical properties of aluminum alloy.The strength and hardness of aluminum alloy can be improved through hot processing.By heating the aluminum alloy at high temperature,the solute atoms in the alloy are evenly dissolved in the matrix to form a solid solution.On the basis of solid solution treatment,the material at appropriate time and temperature to further improve the strength of the material.

3.4.Heat resistance and corrosion resistance

Thermal processing can also improve the heat resistance and corrosion resistance of aluminum alloy.Heat treatment at the appropriate temperature,can make the aluminum alloy to form a relatively stable high-temperature tissue structure,so as to improve the high-temperature resistance of the material.Through heat treatment,the aluminum alloy can form a dense oxide layer,which can prevent the erosion of the external corrosion medium to a certain extent.In addition,heat treatment can also improve the stability of the aluminum alloy grain boundary,reduce the corrosion sensitivity at the grain boundary,so as to further improve the corrosion resistance of the material.

4.Research status and development direction

At present,significant progress has been made on the impact of thermal processing on the organization and properties of aluminum alloy.However,some problems and challenges remain.For example,the optimization of parameters such as deformation temperature,strain rate and deformation degree during thermal machining still needs further study.In addition,the corrosion behavior of aluminum alloy in different environments and its correlation with mechanical properties also need to be further discussed.

The future research direction can include the following aspects:first,to further optimize the thermal processing process parameters to improve the comprehensive performance of aluminum alloy;second,to carry out the corrosion behavior of aluminum alloy in extreme environment to provide theoretical basis for the application of aluminum alloy in complex and harsh environment;third,to explore the thermal processing technology of new aluminum alloy materials to meet the demand of high performance aluminum alloy in different fields.

5.Conclusion

Thermal processing is one of the important processes of aluminum alloy preparation,which has significant influence on the organization and performance of aluminum alloy.By optimizing the thermal processing process parameters,the microstructure of aluminum alloy can be changed effectively and its mechanical properties,heat resistance and corrosion resistance can be improved.The current research has made significant progress,but it still needs further in-depth exploration and optimization.Future research will pay more attention to the application of aluminum alloy in complex environment and its correlation with mechanical properties,to provide theoretical support and technical support for the wide application of aluminum alloy.