DE4417521C2 - Use of an easily machinable aluminum alloy - Google Patents

Description

The invention relates to the use of a readily machinable aluminum alloy of the following composition:
0.7 to 1.4% silicon
up to 0.5% iron
0.2 to 0.51% copper
0.6 to 1.2% magnesium
0.40 to 1.0% manganese
up to 0.3% chromium
up to 0.3% zinc
up to 0.2% titanium
1.5 to 2.0% lead
up to 0.7% bismuth
Impurities individually up to 0.05%, in total up to 0.15%, the rest aluminum for components with a load of up to 200 MPa at temperatures up to 120 ° C for more than 100 hours.

An alloy is often used for components subject to corrosion of the type AlMgSi1 used. However, this is not suitable for Machining on machining centers. For this, alike an addition of chip-breaking elements, preferably lead, such an AlMgSi alloy added to the processing on machines.

From DE-OS 17 58 090 is an aluminum alloy with good Machinability for construction parts or machine elements knows that from 0.01 to 5% titanium, 0.5 to 10% lead, 0.1 to 20% silicon, 0.01 to 10% magnesium, 0.5 to 5% bismuth, 0.1 up to 10% copper, 0.1 to 10% zinc, 0.1 to 5% iron and / or  Manganese and aluminum as the rest. This alloy together The basis is the technical idea, the crystal structure of aluminum and aluminum alloys in the presence of lead and refine titanium to achieve stronger lead increases at higher ones Avoid lead.

There is already a low titanium content of up to 0.05% as an impurity in pure aluminum (see Aluminum Ta schenbuch, 13th edition, page 145), but you need for the Formation of the Al₃Ti crystals indicated as advantageous higher levels than the specified permissible impurities.

An aluminum alloy is known from US Pat. No. 4,589,932 made from 0.4 to 1.2% silicon, 0.6 to 1.1% copper, 0.5 to 1.3% Magnesium, 0.1 to 1% manganese, 0.3 to 0.7% lead and bismuth, up to 0.6% iron, up to 0.1% chromium, up to 0.3% zinc and aluminum the rest with the usual impurities. The well-known Alloy exhibits high strength values after hardening Temperatures of 191 ° C and 204 ° C. From use this alloy for the production of components with a good heat resistance or creep resistance is mentioned in the Literature said nothing. It is only generally stated that the alloys mentioned by extrusion, rolling or other Kneading process can be processed further.

The properties of the known alloys were for the so far manufactured components such. B. ABS housing sufficient because the Components have relatively high wall thicknesses and thus in the Walls only relatively low stresses occurred, which also elevated temperature can be endured without failure of the component could.

Following the general trend for weight loss now the wall thicknesses are reduced so that the stresses in the newly constructed component. At an elevated temperature  The test bench showed that the components met the required requirements Lifetime no longer reached. As a lower limit for that The lifespan of such components becomes a value of viewed at least 100 hours.

The object of the present invention is therefore to find a suitable one Alloy for use in heavy duty aluminum construction propose parts, the maximum effective on the component Tensile stress of z. B. 200 MPa at an operating temperature of e.g. B. 120 ° C over a period of more than 100 hours without Ver say the component should be endured.

The object is achieved by the specified in the claim Features. It has surprisingly been found that in compliance with the alloy composition mentioned Creep resistance can be increased significantly, so that the components made from it are suitable for use at elevated temperatures and even high mechanical chip withstand. So with one Component made of the alloy to be used according to the invention in the creep test at 120 ° C and 200 MPa Stress on smooth and notched samples Breaking times of over 720 hours measured compared to 1.1 hours for the copper-free one AA 6012 alloy under the same test conditions. So that will far exceeded the required lifespan of 100 hours.

Examples from which the limit values for the invention Allow the alloy composition to be used are as follows described. Show it:

Table 1: Chemical composition of the press examined rods (20 × 70 mm) from the 4 different Alloy variants.  

Table 2: Results of the creep tests (break times) of smooth and notched samples (K _t = 1 and K _t = 4.5) in the transverse direction (LT) of the pressing rods (20 × 70 mm) at loads of 160 MPa and 200 MPa and a test temperature of 120 ° C.

Fig. 1: Characteristic tensile test values at room temperature in the longitudinal direction (L) of the pressing rods (20 × 70 mm) as a function of the Cu content.

Fig. 2: Tensile test parameters at room temperature in the transverse direction (LT) of the pressing rods (20 × 70 mm) as a function of the Cu content.

Fig. 3: Creep curves (time expansion curves) of the smooth samples (K _t = 1) in the transverse direction (LT) of the press bars (20 × 70 mm) at 120 ° C and 160 MPa load.

Fig. 4: Creep curves (time expansion curves) of the smooth samples (K _t = 1) in the transverse direction (LT) of the press bars (20 × 70 mm) at 120 ° C and 200 MPa load.

Fig. 5: Influence of the copper content on the minimum creep speed of smooth samples (K _t = 1) in the transverse direction (LT) of the pressing rods at loads of 160 MPa and 200 MPa and a test temperature of 120 ° C.

There were initially cast ingots with those given in Table 1 chemical compositions. These bars were homogenized at a temperature of 480 ° C for 12 hours and then pressed to rectangular bars of the format 70 × 20 mm. The The bar and recipient temperature was 480 ° C.  

The rods were then heat-treated by

• - Solution annealing at 530 ° C in the salt basin for 10 minutes and on final quenching in water at room temperature
• - stretching by 2% plastic stretch
• - thermal expansion at 160 ° C for 16 hours.

The tensile test parameters of the thermally hardened bars as a function of the copper content were shown graphically in Figure 1 and Figure 2. It can be seen that the strength values increase continuously with increasing copper content, while the elongation at break remains almost constant. The strength and elongation at break level in the transverse direction of the bar (LT) is 30 MPa or 2% lower than in the longitudinal direction of the bar (L).

The creep tests were carried out on smooth (K _t = 1) and notched (K _t = 4.5) samples from the critical transverse direction of the bar (LT) in accordance with DIN 50118. The samples were loaded at a temperature of 120 ° C with 160 MPa and 200 MPa, respectively.

The results of the creep tests are summarized in Table 2 set. It turns out that with a copper addition of 0.34 % By weight in comparison to the copper-free AA6012 variant longer life (breaking time) under the load of 200 MPa in unc notched condition by an order of magnitude of 33.4 hours 355.7 hours and even two orders of magnitude when notched increases from 0.2 hours to 24.6 hours. Another Increasing the copper content to 0.51 wt .-% causes in the notched and notched condition under the load of 200 MPa one Life span increased to more than 720 hours. With that the required values for the lifespan of 100 hours far exceeded.  

In Figure 5 are plotted in the linear range of the creep curves (Figure 3 and 4) certain minimum creep in logarithmic scale mixers via the copper content. This shows that the values for the load of 160 MPa and 200 MPa are each on a straight line. At a load of 200 MPa, the creep speed decreases by three powers of ten with increasing copper content up to 0.51% by weight. At a load of 160 MPa, the straight line is shifted by approximately a power of ten to lower minimum creep speeds and has the same slope as at a load of 200 MPa. The copper additive thus not only increases the service life, but also the resistance to creep deformation.

Table 2:

Results of the creep tests (break times) of smooth and notched samples (K _t = 1 and K _t = 4.5) in the transverse direction (LT) of the pressing rods (20 × 70 mm) at loads of 160 MPa and 200 MPa and a test temperature of 120 ° C

Claims (1)

Use of a readily machinable aluminum alloy with the following composition:
0.7 to 1.4% silicon
up to 0.5% iron
0.2 to 0.51% copper
0.6 to 1.2% magnesium
0.40 to 1.0% manganese
up to 0.3% chromium
up to 0.3% zinc
up to 0.2% titanium
1.5 to 2.0% lead
up to 0.7% bismuth
Impurities individually up to 0.05%, in total up to 0.15%, balance aluminum
for components with a load of up to 200 MPa at temperatures up to 120 ° C for more than 100 hours.