Manufacturing method for 7000-series aluminum alloy profile for automobile body

Abstract

The invention provides a manufacturing method for a 7000-series aluminum alloy profile for an automobile body. Raw materials comprises the following alloy elements in percentage by mass: 0.119 to 0.138 percent of Si, 0.148 to 0.17 percent of Fe, 0.05 to 0.19 percent of Cu, 004 to 0.10 percent of Mn, 0.72 to 0.99 percent of Mg, 0.05 to 0.10 percent of Cr, 5.55 to 6.0 percent of Zn, 0.15 to 0.22 percent of Zr and 0.02 to 0.04 percent of Ti, wherein the content of a single element is less than or equal to 0.05 percent; the total amount of other elements is less than or equal to 0.15 percent; thebalance is aluminum; the ratio of Zn to Mg is controlled to be 6 to 8; and the processing process comprises the following treatments of smelting, performing purifying treatment, casting into a bar, performing homogenizing annealing, extruding, cooling, drawing, performing natural aging and performing artificial aging. The profile obtained by the manufacturing method provided by the invention has super-high strength mechanical properties and good corrosion resistance, fatigue resistance and crushing resistance, and is very suitable for batch production of parts, such as an aluminum alloy energyabsorption box, a front longitudinal beam, a rear longitudinal beam, a threshold and an automobile door anti-collision beam, used by an automobile bumper system.

Description

technical field [0001] The invention relates to the field of aluminum alloy materials, in particular to a method for manufacturing high-strength 7000 series aluminum alloy profiles for automobile bodies. 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 refi...

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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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