1 Foreword
2 series aluminum rod -2017 is the first hard aluminum alloy in the industry of Al-Cu-Mg alloy, its composition is reasonable, and the overall performance is better. Off-line quenching is used in natural aging conditions. However, the off-line quenching process is relatively cumbersome, and the performance requirements of the heat treatment equipment are also relatively high, and the off-line quenching can easily cause local grain coarsening of the bar material, and the off-line solution temperature can easily cause insufficient hardness. In this paper, the method of reverse extrusion in-line quenching+pulling+artificial aging is studied to produce high-precision, high-hardness 2017 alloy bar. The effect of different heat treatment processes and drawing processing rate on the performance of 2017 alloy bar is discussed. Through the optimization of heat treatment and drawing process, we have produced products that meet the requirements of customers.
Product technical requirements: alloy grade 2017, product diameter φ27.1 ± 0.2mm, hardness ≥ Hv135, delivery length: 2500mm, bending degree: ≤ 0.6mm/2500mm.
2 Reverse extrusion design legend
3 Production Process
3.1
chemical composition
Through the optimal design of the alloy, the chemical composition of the aluminum rod is controlled as shown in Table 1:
Table 1 2017 alloy composition
3.2
Extrusion process
Ingot blank specifications: φ130 × 205mm, 1100 tons of single-acting inverse extrusion machine into two bars φ28.5mm and φ27.8mm specifications. Extrusion process parameters are shown in Table 2:
Table 2 extrusion process parameters
3.3
Heat treatment
The effects of on-line quenching+natural aging, natural aging+artificial aging, natural aging+drawing+artificial aging, and its effect on product hardness and bending were investigated.
3.4
Drawing processing rate
The φ28.5mm and φ27.8mm aluminum rods were drawn to φ27.1mm bars using different machining rates to verify the effect of different processing rates on the hardness and bending of the products.
4 Test plan
The φ28.5mm and φ27.8mm rods that have been subjected to reverse extrusion in-line quenching are experimentally investigated in the following manner during the production process.
4.1 The extruded bars were aged for 2 h, 5 h, 10 h, 24 h, 36 h, 48 h, 72 h, and 110 h, and the hardness after natural aging was measured.
4.2 After natural aging for 2.5 h and 36 h, artificial aging was performed again to examine the effect on the hardness of subsequent artificial aging.
4.3 The natural aging of the bar after the "pull + artificial aging" deformation heat treatment, testing its impact on the hardness;
4.4 The effect of different drawing processing rates on hardness and bending of bars was examined.
5 Experimental results and analysis
5.1 Natural aging test after extrusion quenching
Take 10 quenched bars with diameter of φ27.8±0.10mm online and place them for 2h, 5h, 10h, 24h, 36h, 48h, 72h, and 110h for natural aging. Measure their hardness, and draw the natural aging hardness curve as shown in Figure 3 .
Fig. 3 Natural aging hardening curve of 2017 aluminum rod
It can be seen from Fig. 3 that after online quenching of the 2017 alloy extruded bar, the natural ageing reaches the peak hardness for 3 days, and the maximum hardness can reach Hv120 or so.
5.2 Artificial aging after natural aging
Take in-line water-cooled quenching, diameter 27.8 ± 0.10mm bar sample 20, the natural aging 2.5h, 36h, and then (170 °C × 8h) artificial aging, the measured hardness in Table 3.
Table 3 Hardness of Artificial Aging after 2017 Aging
From the data in Table 3, it can be seen that the final hardness achieved by artificial aging for 2.5 hours or 36 hours after natural aging is basically the same as the peak hardness achieved by natural aging.
5.3 Natural aging after drawing and artificial aging test
Thirty-six bar samples with a diameter of φ27.8±0.10mm were sampled in water-cooled and quenched in-line, and then natural ageing was performed for 2h, 18h, and 42h respectively. After drawing, the bar was made into a gauge φ27.1mm, and artificial aging was performed at (170°C×8h). The measured hardness is shown in Table 4.
Table 4 Hardness of 2017 Aluminum Rod after Natural Ageing
From Table 4, it can be seen that when the drawing processing rate is not changed, the natural aging time can increase the bar hardness after “pulling+artificial aging”, and after 18 hours natural aging, the “drawing+artificial aging” hardness is performed. Values can meet product specifications.
5.4 Effect of Drawing Rate on Hardness of Bars
Take 10 rods of diameter φ28.5mm and φ27.8mm, natural aging 18h after drawing into φ27.1mm, the processing rate was 15.3%, 8.2%, and then artificial aging (170 °C × 8h), respectively, measured The average hardness is shown in Figure 4.
Figure 4 Effect of different drawing rates on the final hardness of 2017 aluminum rods
5.5 Experiment on the effect of drawing rate on bending rate
When the φ28.5mm bar was pulled once to a φ27.1±0.2mm product, the processing rate was 15.3%. Due to the excessive processing rate, the residual stress of the product is large, the surface of the product is easily scratched, and the product is severely bent. After repeated straightening, the bending requirement cannot be satisfied.
After the switch to three-pass drawing process: the first pass from φ28.5mm drawn into φ27.9mm, the second pass from φ27.9mm drawing φ27.4mm, the third pass from φ27.4mm drawn into φ27. 1±0.2mm, the processing rate was 6.7%, 5.8%, and 3.6%, respectively. Although the scratch on the surface of the product was reduced and the bending was improved to a certain extent, the pass rate of the product was still very low, only 35.6. %qualified.
While taking 27 pieces of 27.8mm diameter bars into a φ27.1±0.2mm product at a time, the processing rate was 8.2%. After straightening, the finished product was sawed into 2500 mm. All the bending tests were qualified. The results are shown in Table 5.
Table 5 2017 aluminum rod bending test results
6 in conclusion
From the perspective of simplifying the production process and optimizing the production process, this article focuses on the methods for producing high-precision and high-hardness 2017 alloy bars under different heat treatment processes and different drawing processing rates.
6.1 Under the above extrusion process conditions, the maximum hardness value of natural alloys after quenching on-line quenched by 2017 alloys can only reach about Hv120 after 3 days. Artificial aging after natural aging has no obvious effect on hardness.
6.2 Extend the natural aging time before bar drawing, can increase the artificial aging hardness after drawing.
6.3 Increasing the drawing processing rate can increase the product hardness after artificial aging.
6.4 Under the same drawing conditions, the drawing processing rate has an effect on the bending of the product. The greater the processing rate, the greater the bending;
6.5 Extrusion outlet temperature controlled φ27.8mm extrusion billet that is quenched online above 470°C, after natural aging for more than 18h, once drawn into φ27.1±0.02mm bar, and then artificial aging (170°C×8h), Can achieve HV ≥ 135, straightness ≤ 0.6mm/2500mm technical requirements.
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