Method and system for producing aluminum alloy parts

Abstract

In production of aluminum alloy members by a plastic working of a heat-treatable aluminum alloy extrusion, cracking during the plastic working is eliminated or minimized at low cost as compared with techniques including solution treatment or restoration treatment. An aluminum alloy production system includes an extruding press, a cutting device disposed downstream from the extruding press, and a conveyer and a plastic working machine each disposed in parallel with the extruding press. The extruding press hot-extrudes a heat-treatable aluminum alloy to give an extrusion. The cutting device cuts the extrusion to a predetermined length and isolates the extrusion from the extruding press. The conveyer conveys the extrusion to the plastic working machine, where the extrusion has been cut by the cutting device to a predetermined length. The plastic working machine imparts a plastic working to the extrusion conveyed by the conveyer to form the extrusion into an aluminum alloy part.

Description

FIELD OF INVENTION[0001]The present invention relates to a method for producing aluminum alloy parts through plastic working of heat-treatable aluminum alloy extrusions, and to a production system suitable for carrying out the method.BACKGROUND OF INVENTION[0002]Automobile parts such as collision protectors (e.g., bumper reinforcements) and body frames require higher strengths due to recent enhancement of automobile crash safety standards and pedestrian protection standards. On the other hand, the automobile parts also require lower weights due to demands for higher maneuverability and higher fuel efficiency. To have higher strengths and lower weights, some of these automobile parts are made from heat-treatable aluminum alloy extrusions. The extrusions may undergo a plastic working such as bending or crushing for higher design freedom and smaller number of parts.[0003]An exemplary conventional method and system for producing an aluminum alloy member (a bumper reinforcement, herein) ...

AI Technical Summary

Benefits of technology

[0022]To resolve the disadvantages, the extrusions have to undergo canceling of natural age hardening to have lower yield strengths and higher elongations before plastic working. To cancel the natural age hardening of the extrusions, the solution treatment and restoration treatment as described above are considered as a possible solution. Disadvantageously, however, these treatments require reheating and cooling of the extrusions immediately before plastic working, and this causes increased spending on heat treatment facilities and additional steps and causes increased cost.

[0024]The present invention has an object to eliminate or minimize cracking during plastic working at low cost as compared with a technique including solution treatment or restoration treatment, in production of aluminum alloy members through plastic working of heat-treatable aluminum alloy extrusions.

[0025]The present invention has another object to allow extrusions to less deform after cooling and to allow inner ribs to have higher strengths after artificial aging, when the heat-treatable aluminum alloy extrusions have a hollow section and include one or more inner ribs.

[0030]With the aluminum alloy part production method according to the embodiment of the present invention, the extrusion extruded from the extruding press and moving forward is cut in situ to a predetermined length, conveyed to the plastic working machine, and undergoes a plastic working before progress of natural aging (before the yield strength exceeds 120 MPa), without being stocked on a table or in another storage area. This configuration allows the extrusion to undergo a variety of plastic working while maintaining a low yield strength and a high elongation and to resist cracking during the plastic working, without solution treatment and restoration treatment performed before the plastic working. The production method eliminates the need for solution treatment and restoration treatment, provides a low yield strength upon plastic working, and can produce aluminum alloy parts having low springback and high precision with low cost. In addition, the production method can reduce residual stress accompanied with pressing and allows the resulting aluminum alloy parts, even when being high-strength 7xxx-series aluminum alloy members, to have better stress corrosion cracking resistance.

[0031]The heat-treatable aluminum alloy extrusion extruded from the die is quenched by natural cooling or forced cooling (such as fan air cooling or water cooling). Assume that the extrusion has a hollow section and includes inner ribs in the cross section. In this case, the method may also employ cooling by a nozzle that injects a coolant employed as a cooling mechanism. This configuration allows the extrusion to cool not only from the outside of the cross section, but also from the inside thereof and to have lower temperature difference in the entire cross section in the cooling process. This allows the extrusion to less deform by thermal shrinkage during cooling, to have lower temperature history difference within the cross section, and, after temper aging, to have material properties that are uniform within the cross section. The combination use of the nozzle allows the extrusion to cool at a higher cooling rate and to be quenched even when the material alloy is an aluminum alloy having high quench sensitivity, such as a high-strength 7xxx-series aluminum alloy. This promises still higher strength of the extrusion after temper aging.

Problems solved by technology

Unfortunately, the extrusions have lower elongations due to progress of natural aging and suffer from rupture and / or cracking when undergoing plastic working with large deformation.

This disadvantageously causes lower dimensional accuracy.

The aluminum alloys suffer from these disadvantages more with an increasing strength of the materials (alloys).

Disadvantageously, however, these treatments require reheating and cooling of the extrusions immediately before plastic working, and this causes increased spending on heat treatment facilities and additional steps and causes increased cost.

Disadvantageously, however, the inner ribs, which are not directly cooled from the outer periphery, undergo insufficient quenching due to delayed temperature fall, and the extrusions fail to have a predetermined strength after artificial aging.

In addition, the extrusions after cooling disadvantageously have large deformation due to difference in thermal shrinkage, because of uneven temperature distribution in the cross section during cooling.

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