Simulation of initial cooling rate effect on the extrudate distortion in the aluminum extrusion process

The cooling process after aluminum extrusion is crucial for the strengthening of AlMgSi-type alloys but can induce distortions caused by fast cooling, especially for complex or critical sections. The optimum cooling conditions fall within the so-called quench window between two limitations (high strength and lower distortion). Appropriate modeling, using both physical and numerical methods, can guide us to achieve a better cooling strategy in extrusion plants. In this paper, we focus on the study of the optimal strategy of the initial cooling for selected cases. A simple extruded section in the actual scale was simulated by a reasonably realistic numerical model. The section was cooled by a water spray from one side (top side) and still air on the other side. The effect of the initial cooling was evaluated by defining a measure called the “front width”, and the distortion mechanism for different front widths was studied. The effect of some selected parameters (e.g., the thickness, the stop time and the extrusion speed) were also taken into consideration. The simulation results showed that a combination of distortion stages (concave or convex) played a main role in determining the final shape and distortion magnitude. If the process parameters (e.g., the front width, extrusion speed and others) are set in such a way that could restrict the accumulation of distortions at subsequent zones, then the section suffers fewer distortions. For example, if the cooling begins sharper the extrudate suffers smaller distortion. A longer stop time is beneficial for less distortion when it is long enough to ensure that the section in the cooling zone is cooled to room temperature. The extrusion speed has varying effects and could be optimized for any profile thickness. However, even when optimizing the other parameters, the thicker section might be distorted more than the thinner section.