Improvement of microstructure and properties in twin-roll casting 7075 sheet by lower casting speed and compound field

Abstract

Well-developed dendrites and severe macro and micro segregations in 7075 sheet produced by horizontal twin-roll casting (TRC) deteriorates the hot-workability and properties of the sheet, which makes an obstacle for the successful use of this technology. In this paper, lower casting speed and a pulsed electric-magnetostatic compound field are used to refine microstructure and abate segregation in TRC 7075 sheet. The dendrite arm space decreases from 20 ¿m to 8¿13 ¿m and the micro-segregation degree of Mg, Zn and Cu decreases when casting speed decreases from 1.5 m/min to 0.75 m/min. The center macro-segregation belt disappears in the 0.75 m/min sheet. The as-cast structure and the dendritic segregation in the 0.75 m/min sheet are further refined and abated respectively by the compound field. The secondary dendrite arm size decreases to 5¿8 ¿m in the field sheet. The 0.75 m/min sheet casted with the field shows better mechanical properties after homogenization and hot rolling. The optimization mechanism of lower casting speed and the field was discussed with the aid of classical solidification theory and electromagnetism.

A Novel Approach to Improve the Microstructure and Mechanical Properties of Al–Mg–Si Aluminum Alloys during Twin-Roll Casting

“…Yun et al have shown a graph where the strip thickness is plotted versus the specific rolling force (i.e., the total load applied divided by the strip width). If all the experimental results under different processing conditions are collected together, it is possible to build a convenient "defect limit diagram" to predict the relationship between processing technology and segregation defects [2][3][4].…”

“…However, it soon became obvious that the technology introduced some features in the finished product that limited its use compared with conventionally produced materials. The most serious disadvantage is that when the aluminum alloy with high alloy element content is produced by twin-roll casting method, because of its wide solidification range, the centerline segregation defects easily occurred in the casting rolling strip, which makes the twin-roll cast products crack in the subsequent processing [4]. Therefore, it is urgent to develop a novel method to produce aluminum alloy of wide solidification range with fewer segregation defects and better properties, which has the prospect of engineering application.…”

Annealing of Al-Zn-Mg-Cu Alloy at High Pressures: Evolution of Microstructure and the Corrosion Behavior

“…However, it may lead to large dendritic microstructures, shrinkage during solidification, etc. [ 6 , 7 ], which severely retard the application of this alloy. To improve the performance of Al-Zn-Mg-Cu-based alloys, strategies such as alloy modification [ 8 , 9 ] and homogenization treatment [ 10 , 11 ] have been adopted.…”

Microstructure as an essential aspect of EN AW 7075 aluminum alloy quality influenced by electromagnetic field during continuous casting process

“…It was proposed that the required features of an ingot can be achieved by adjusting the performance parameters, having in mind the relation between the microstructure and mechanical characteristics [17]. Since the EN AW 7075 aluminum alloy is well known for its remarkably high strength, which is widely applied in aircraft and military industries, it continues to challenge researchers to achieve improvements by application of different casting techniques [18] or heat treatment procedures [19].…”