Automobile body part

Abstract

In a car body or component thereof with at least one first component of sheet metal of a first aluminum alloy and at least one second component of sheet metal of a second aluminum alloy, the first and second aluminum alloys are of type AlMgSi and in the sheet metal of the second aluminum alloy a substantial part of the elements Mg and Si, which are required to achieve artificial ageing in solid solution, is present in the form of separate Mg.sub.2Si and/or Si particles in order to avoid artificial ageing. By reduction of the hardening capacity of the second component during artificial ageing of the body as part of the paint baking cycle, the car body has an improved impact protection for pedestrians in comparison with solutions according to the prior art.

Claims

1. An automobile body or component thereof comprising at least a first sheet metal component of a first aluminum alloy (A) and at least a second sheet metal component of a second aluminum alloy (B), whereby the first and second aluminum alloys are AlMgSi type aluminum alloys and, after artificial ageing of the body or component thereof, the second sheet metal component has a lower mechanical strength than the first sheet metal component, wherein at least the first aluminum alloy component (A) contains: 0.6 to 1.2 weight percent silicon; 0.3 to 0.8 weight percent magnesium; max. 0.8 weight percent copper; max. 0.4 weight percent iron; max. 0.3 weight percent manganese; max. 0.2 weight percent vanadium; and production-related contaminants with aluminum as the remainder, and wherein at least in the second sheet metal component of the second aluminum alloy (B), a substantial part of the elements Mg and Si, which are required to achieve artificial ageing in solid solution, are present as separate Mg.sub.2Si and/or Si particles before artificial ageing of the body or body part in order to avoid artificial ageing, and wherein the second sheet metal component of the second aluminum alloy (B) has a yield strength of 60 MPa or less.

2. The automobile body or component thereof of claim 1, wherein at least in the second sheet metal component of the second aluminum alloy (B) at least more than 40% of the elements Mg and Si are precipitated in a form where they are no longer available for subsequent artificial aging.

3. The automobile body or component thereof of claim 1, wherein the second aluminum alloy (B) contains: 0.30 to 0.50 weight percent silicon; 0.30 to 0.50 weight percent magnesium; max. 0.20 weight percent copper; 0.05 to 0.20 weight percent iron, max. 0.10 weight percent manganese; max. 0.15 weight percent vanadium; with production-related contaminants, individually a maximum of 0.05 weight percent, total maximum of 0.15 weight percent, and aluminum as the remainder.

4. The automobile body or component thereof of claim 3, wherein vanadium in the second aluminum alloy (B) is 0 weight percent.

5. The automobile body or component thereof of claim 1, wherein the second sheet metal component is a bonnet, an inner panel of a body part, in particular a hood, or a trim part, a structural component or a reinforcing element in the front part of an automobile body.

6. The automobile body or component thereof of claim 1, wherein the second sheet metal component is a deep-drawn body part with good bending behavior.

7. An automobile body or component thereof comprising at least a first sheet metal component of a first aluminum alloy (A) and at least a second sheet metal component of a second aluminum alloy (B), whereby the first and second aluminum alloys are AlMgSi type aluminum alloys and, after artificial ageing of the body or component thereof, the second sheet metal component has a lower mechanical strength than the first sheet metal component, wherein at least the first aluminum alloy component (A) contains: 0.6 to 1.2 weight percent silicon; 0.3 to 0.8 weight percent magnesium; max. 0.8 weight percent copper; max. 0.4 weight percent iron; max. 0.3 weight percent manganese; max. 0.2 weight percent vanadium; and production-related contaminants with aluminum as the remainder; wherein the second aluminum alloy (B) contains: 0.30 to 0.50 weight percent silicon; 0.30 to 0.50 weight percent magnesium; max. 0.20 weight percent copper; 0.05 to 0.20 weight percent iron, max. 0.10 weight percent manganese; max. 0.15 weight percent vanadium; with production-related contaminants, individually a maximum of 0.05 weight percent, total maximum of 0.15 weight percent, and aluminum as the remainder; and wherein at least in the second sheet metal component of the second aluminum alloy (B), a substantial part of the elements Mg and Si, which are required to achieve artificial ageing in solid solution, are present as separate Mg.sub.2Si and/or Si particles before artificial ageing of the body or body part in order to avoid artificial ageing.

8. The automobile body or component thereof of claim 7, wherein at least in the second sheet metal component of the second aluminum alloy (B), at least more than 40% of the elements Mg and Si are precipitated in a form where they are no longer available for subsequent artificial aging.

9. The automobile body or component thereof of claim 7, wherein vanadium in the second aluminum alloy (B) is 0 weight percent.

10. The automobile body or component thereof of claim 7, wherein the second sheet metal component is a bonnet, an inner panel of a body part, in particular a hood, or a trim part, a structural component or a reinforcing element in a front part of the automobile body.

11. The automobile body or component thereof of claim 7, wherein the second sheet metal component is a deep-drawn body part.

12. The automobile body or component thereof of claim 7, wherein the second sheet metal component of the second aluminum alloy (B) has a yield strength of 60 MPa or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram with the yield strength of a first and a second aluminum alloy in different ageing states;

(2) FIG. 2 is a diagram with the differences between the yield strength of the first and second aluminum alloys of FIG. 1 in different ageing states and the yield strength of the alloys in delivery state T4;

(3) FIGS. 3 and 4 are pictures taken from metal cuts of sheet samples with different part of precipitated Mg.sub.2Si particles under a scanning electron microscope (SEM) in compo modus; and

(4) FIG. 5 shows the dependence of the yield strength on the volume part of precipitated Mg.sub.2Si particles of an AlMgSi alloy by means of a model calculation.

DETAILED DESCRIPTION

Example 1

(5) From a first aluminum alloy A (AA 6016) and a second aluminum alloy B with the chemical compositions given in table 1, strips of thickness 1.2 mm were produced in a conventional manner by vertical continuous casting, homogenization annealing, hot and cold rolling.

(6) TABLE-US-00001 TABLE 1 Alloy Si Fe Cu Mr Mg Cr Zn Ti V A 1.14 0.21 0.08 0.07 0.55 0.013 0.003 0.033 <0.005 B 0.42 0.17 0.08 0.07 0.40 0.018 <0.003 0.024 0.006
The strips were subjected to solution annealing (alloy A) and partial solution annealing (alloy B) in a strip passage annealing oven, then quenched by moving air and artificially aged for several days at room temperature to delivery state T4. For the two aluminum alloys A and B the following solution annealing conditions were selected: Alloy A 550° C./30 seconds Alloy B 500° C./20 seconds

(7) A paint baking cycle was simulated on sheet samples of aluminum alloys A and B in delivery state T4, with annealing at a temperature of 185° C. for a period of 20 min. To test the influence of cold forming (CF) on the yield strength R.sub.p0.2, tensile strength R.sub.m and elongation at fracture A.sub.80, the sheet samples in delivery state were 2% further cold formed. A further series of specimens were 2% cold formed in delivery state and then subjected to the above-mentioned annealing treatment.

(8) The mechanical strength values given in Table 2 for the two aluminum alloys A and B in the various states tested, and the values also shown graphically in FIGS. 1 and 2 for the yield strength R.sub.p0.2, for both aluminum alloys A and B in delivery state with 2% cold forming, show a slight and proportionally approximately equal increase in yield strength. If merely a paint baking annealing is performed at the delivery state, for alloy A there is a clear increase in the yield strength whereas for alloy B there is practically no artificial ageing effect. The differing behavior of the two aluminum alloys A and B under paint baking conditions is even clearer under combined application of cold forming 2% with subsequent annealing at 185° C. for 20 minutes, as often occurs in practice in the production of car body parts.

(9) TABLE-US-00002 TABLE 2 R.sub.p0.2 R.sub.m A.sub.80 ΔR.sub.p0.2 Alloy State [MPa] [MPa] [%] [MPa] A A Delivery state T4 115 225 25.4 185° C. × 20 min 195 271 20.8 80 2% CF 140 251 24.3 25 2% CF + 185° C. × 20 min 245 295 15.4 130 B A Delivery state T4 70 129 27.7 185° C. × 20 min 74 130 25.9 4 2% CF 90 133 25.3 20 2% CF + 185° C. × 20 min 94 149 18.6 24

Example 2

(10) On 2 tensile test pieces of alloy B in Example 1 having a thickness of 0.85 mm and a width of 12.5 mm in different artificial ageing conditions tensile strength R.sub.m, yield strength R.sub.p0.2 and elongation at fracture A.sub.50 have been determined in tensile tests. The examined artificial ageing treatments are given in Table 3. The solution annealing was carried out in a salt bath at the given temperature for the given time. Subsequently the test pieces were quenched in water, aged for 24 h at room temperature and subsequently aged for 24 h at a temperature of 65° C. This ageing treatment leads to a simulated T4 condition. A part of these test pieces A to L was given an artificial ageing treatment at 205° C. for 1 h, corresponding to a T6 condition.

(11) TABLE-US-00003 TABLE 3 Test Piece Solution annealing A 520° c./5 s B 520° c./10 s C 530° c./0 s D 530° c./5 s E 530° c./10 s F 530° c./20 s G 540° c./0 s H 540° c./5 s I 540° c./10 s J 540° c./20 s K 540° c./60 s L 540° c./10 min

(12) The results of tensile tests carried out on 2 test pieces each are given in Table 4 for the test pieces in the T4 condition and in Table 5 for the test pieces in the T6 condition.

(13) TABLE-US-00004 TABLE 4 Test piece R.sub.p0.2 [MPa] R.sub.m [MPa] A.sub.50 [%] A1 43.9 115.6 16.3 A2 44.6 114.5 23.3 B1 43.9 114.9 20.2 B2 44.2 117.3 23.2 C1 44.1 116.4 24.2 C2 40.6 112.9 26.8 D1 45.2 114.8 30.9 D2 43.6 116.0 22.0 E1 44.0 119.5 15.6 E2 45.3 117.2 25.5 F1 48.5 125.2 19.0 F2 48.4 124.9 26.6 G1 41.5 112.1 26.1 G2 42.9 111.1 25.1 H1 43.7 115.3 25.1 H2 43.9 114.0 20.2 I1 44.0 119.0 21.7 I2 45.3 118.7 24.9 J1 48.3 127.6 15.1 J2 47.6 126.1 24.4 K1 56.8 137.8 15.6 K2 56.4 137.9 16.2 L1 63.1 152.4 20.7 L2 61.7 144.1 18.1

(14) TABLE-US-00005 TABLE 5 Test piece R.sub.p0.2 [MPa] R.sub.m [MPa] A.sub.50 [%] A1 47.1 117.2 25.1 A2 46.5 116.1 21.6 B1 52.5 119.9 24.8 B2 54.3 123.4 25.3 C1 40.9 111.0 26.1 C2 41.4 111.2 27.9 D1 49.9 119.6 24.4 D2 53.2 120.4 25.2 E1 50.6 121.4 25.3 E2 57.2 123.5 23.9 F1 61.5 130.9 24.7 F2 61.7 129.1 22.9 G1 44.7 114.1 28.1 G2 44.0 113.3 26.5 H1 45.4 119.9 20.5 H2 47.5 118.4 19.2 I1 55.6 125.7 25.0 I2 52.6 124.5 25.4 J1 65.9 135.1 18.5 J2 64.5 135.1 18.9 K1 98.3 154.6 10.6 K2 98.2 153.5 11.3 L1 138.4 177.3 9.0 L2 137.4 178.0 11.4

(15) From the test pieces C and L in table 4 metal cuts have been made. Under a scanning electron microscope in the compo modus the volume part of the precipitated Mg.sub.2Si particles related to the total volume has been determined by measuring the corresponding area parts in 12 area regions. Particles having a diameter <0.1 μm are designated as precipitated Mg.sub.2Si particles.

(16) The mean values for the test piece C resulted in a volume part of 0.444.+−.0.077% corresponding to apart of about 50% of the theoretically possible Volume part. For the test piece L the mean values resulted in a volume part of 0.071.+−.0.029% corresponding to a part of about 8% of the theoretically possible volume part.

(17) The SEM picture in compo modus of test piece C shown in FIG. 3 and of test piece L shown in FIG. 4 let the heavy iron containing precipitates appear as bright spots and the light-weight Mg.sub.2Si particles as dark spots. The higher volume part of precipitated Mg.sub.2Si particles of test piece C in comparison with test piece L is clearly perceptible.

(18) With the values for the yield strength R.sub.p0.2 measured on the test pieces A to L of Table 5 the dependence of the yield strength R.sub.p0.2 on the volume part of the precipitated Mg.sub.2Si particles has been determined by means of a model calculation and is graphically shown in FIG. 5. The values on the x-axis correspond to the ratio of the volume part of the Mg.sub.2Si pre-precipitates to the theoretically possible volume part.

(19) The diagram clearly shows that the yield strength R.sub.p0.2 selected here as a measure for the “softness” of the alloy can be varied within broad limits by controlling the pre-precipitation of Mg.sub.2Si.