High-strength 7000-series aluminum alloy profile for automobile body and manufacturing method of high-strength 7000-series aluminum alloy profile

Abstract

The invention provides a high-strength 7000-series aluminum alloy profile for an automobile body. The high-strength 7000-series aluminum alloy profile is prepared from the raw materials in percentageby mass: 0.1%-0.17% of Si, 0.14%-0.17% of Fe, 0.05%-0.30% of Cu, 0.04%-0.10% of Mn, 0.6%-1.0% of Mg, 0.03%-0.10% of Cr, 5.5%-6.0% of Zn, 0.15%-0.25% of Zr, 0.01%-0.04% of Ti, less than or equal to 0.05% of other individual elements, less than or equal to 0.15% of other elements in total, and the balance of Al. The invention further provides a manufacturing method of the high-strength 7000-series aluminum alloy profile for the automobile body. The room-temperature tensile mechanical properties of the profile can realize the tensile strength R<m> of greater than 370 MPa, R<p0.2> of greater than350 Mpa and A50 of greater than 15%; and the static crushing properties can reach the maximum crushing force of greater than 480 kN, the average crushing force of greater than 350 kN and the absorbedenergy of greater than 70 kJ. The profile simultaneously has ultrahigh-strength mechanical properties and good corrosion-resistant, anti-fatigue and crushing properties and is very suitable for mass production of components such as an aluminum alloy energy absorbing box, front and rear longitudinal beams, a door sill and an automobile door anti-collision beam of an automobile bumper system.

Description

technical field [0001] The invention relates to the field of aluminum alloy materials, in particular to a high-strength 7000 series aluminum alloy profile for automobile bodies and a manufacturing method. Background technique [0002] 7000 series (Al-Zn-Mg-Cu) aluminum alloy profiles are widely used in aerospace, high-speed rail and high-end automobile manufacturing and other fields. The production of such aluminum alloy profiles generally includes: melting, casting, homogenization, extrusion, natural Aging, bending weld forming and artificial aging heat treatment. [0003] The 7000 series aluminum alloys tend to form relatively coarse grain structure and coarse eutectic structure during the casting process. The reasons for the formation of the coarse grain structure are generally divided into two categories: (1) The casting temperature is too high or the holding time of the aluminum liquid is too high. Long, so that there are fewer nucleation particles and uneven grain ref...

AI Technical Summary

Problems solved by technology

[0003] The 7000 series aluminum alloys tend to form relatively coarse grain structure and coarse eutectic structure during the casting process. The reasons for the formation of the coarse grain structure are generally divided into two categories: (1) The casting temperature is too high or the holding time of the aluminum liquid is too high. Long, so that there are fewer nucleation particles and uneven grain refinement effect during solidification, resulting in grain growth; (2) Insufficient cooling intensity leads to low solidification supercooling degree, resulting in coarse grain structure

[0011] (3) The casting process parameters are unreasonable: the addition method and time of the master alloy need to be improved. For example, the addition of Cu element in the early stage of smelting will easily cause uneven melting, and the Al-Mg master alloy will burn seriously and easily produce MgO oxide film. Added at the beginning of smelting

The heat preservation time is not strict enough, and the heat preservation time is much longer than 20-30 minutes, which is easy to cause hydrogen absorption and heavy element precipitation

If the casting temperature is too high, the cooling strength will be insufficient, resulting in the lack of time to cool the center of the cast aluminum rod to form a coarse eutectic structure and large-grained inclusion phase, which will reduce the processing, welding, fatigue and crushing properties of the material

[0012] (4) The homogenization process is unreasonable: At present, a high-temperature short-time single-stage or two-stage homogenization heat treatment process is generally used, and the homogenization furnace cannot achieve gradient temperature rise, resulting in Al that can inhibit recrystallization 3 Zr particles cannot be uniformly dispersed and precipitated

[0013] (5) The parameters of the extrusion process are unreasonable: the extrusion temperature is too low, the surface quality of the extruded product is poor, and the extrusion speed is too slow, resulting in a sharp decrease in the life of the die and cracking at the bridge position of the die; if the extrusion temperature is too high, dispersed precipitation Al 3 Zr loses the effect of inhibiting recrystallization, the outlet temperature of the material exceeds its solidus line, the coarse grain layer on the surface increases, the material is over-burned, and the comprehensive performance decreases sharply, which cannot realize the collision safety and fatigue corrosion resistance in the whole life cycle of automotive alloys. sex;

[0014] (6) Unreasonable heat treatment and design of extrusion die material selection: Forged and remelted H13 hot work die steel or CrMnMo is not selected as the extrusion die material, and the spheroidizing annealing temperature of forging is too high, causing loose material structure; Choose oil quenching or quenching medium with low cooling rate; unreasonable design of heat treatment and tempering times, unreasonable control of tempering temperature and time at each stage; large number of welding lines in extrusion die design, resulting in increased number of bridge positions; The design of the bridge position follows the traditional design idea, which is thick and the diversion groove is not smooth enough; resulting in severe coarse grains at the welding line of the extruded profile, high mechanical properties and poor toughness, and obvious reduction in bending and welding performance, which is not conducive to the final parts comprehensive performance

[0015] (7) The heat treatment process is unreasonable: the final aging heat treatment can be carried out in various processes such as T6 / T79 / T76 / T73. Most manufacturers do not understand the aging process clearly, resulting in their materials failing to meet the performance requirements of automotive alloys; Impact toughness, weldability and bend formability can also vary considerably under the same conditions

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