High hardness moulding plate and method for producing said plate

Abstract

Moulding plate of an aluminium wrought alloy including, in weight percent: Si 1.4-2.1, Mn 0.8-1.2, Cu 0.45-0.9, Mg 0.7-1.2, Ti <0.15, Zn <0.4, Fe <0.7, one or more of Zr, Cr, V each <0.25, incidental elements and impurities, each <0.05, total <0.25, the balance aluminium, and having a thickness of more than 0.6 mm and in T6 temper condition having a hardness of more than 105 HB. A method of making the plate is also disclosed.

Description

CROSS REFERENCE TO RELATED APPLICATION

This claims priority from European patent application no. 04077781.7, filed 5 Oct. 2004, incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to moulding plate of an aluminium wrought alloy. The invention further relates to a method for producing said moulding plate.

BACKGROUND OF THE INVENTION

In the tooling and moulding plate market for blow moulding and thermoforming of rubbers and plastic, a sustained effort in reducing costs is made whilst maintaining satisfactory wear resistance and repair weldability. These types of tooling plates are also widely used in many other industrial applications, including components produced by various machining operations such as drilling, milling and turning. Commonly used tooling plates are made from selected alloys from the AA2000 series alloys, the AA6000 series alloys or the AA7000-series alloys.

High wear resistance in combination with good machinability are important properties of alloys for moulding plate. In typical tooling plate wrought alloys this wear resistance is obtained by alloying with copper (such as in the AA2000 series) or Zinc (such as in the AA7000 series) or magnesium and silicon (such as in the AA6000 series) in combination with a thermo-mechanical treatment. In these heat treatable alloy classes, the typical way to achieve high hardness is via precipitation hardening of coherent phases. Additional hardening by relatively coarse particles, such as primary Si and incoherent Mg₂Si is often considered inappropriate, because of the related risks of eutectic melting at elevated temperatures. Also additional hardening by α-Al(Fe,Mn,Cu)Si dispersoids is not readily applied, since it is generally believed that they increase the quench sensitivity of the alloy. Increased quench sensitivity is considered a disadvantageous characteristic, in particular for thicker gauge products.

Typically, with AA2000 and AA7000 alloys, higher hardness is achieved than with AA6000 alloys. However, a disadvantage of the AA2000 series is the high copper content which makes the alloy expensive as well as very sensitive to the heat treatment. Also, the weldability of the alloy is adversely affected by the high copper content. Similar arguments are made for the AA7000 series such as high residual stresses, and poor weldability and corrosion performance which cause complications with dimensional tolerances, repair weldability, and durability of the mould. The wear resistance of an AA6000 series alloy in a T6 temper, such as AA6010, AA6013, AA6061, AA6066, AA6070 and AA6082 is usually adequate for normal industrial applications. However, for high performance applications a higher wear resistance is desired, without adversely affecting weldability and costs.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a moulding plate of an aluminium wrought alloy with an improved resistance to wear.

The present invention provides a moulding plate of an aluminium wrought alloy comprising, in weight percent: Si 1.4-2.1, Mn 0.8-1.2, Cu 0.45-0.9, Mg 0.7-1.2, Ti <0.15, Zn <0.4, Fe <0.7, one or more of Zr, Cr, V each <0.25, incidental elements and impurities, each <0.05, total <0.25, the balance aluminium, and having a thickness of more than 0.6 mm and in T6 temper condition having a hardness of more than 105 HB.

According to a further aspect of the invention, a method is provided of manufacturing a moulding plate.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1, which is the sole figure, shows the hardness profiles of plates with a composition according to Example 7 with thicknesses of 80, 100 or 150 mm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, the above-mentioned object is reached by providing a moulding plate of an aluminium wrought alloy comprising, in weight percent:

Si 1.4-2.1

Mn 0.8-1.2

Cu 0.45-0.9

Mg 0.7-1.2

Ti <0.15

Zn <0.4

Fe <0.7

one or more of Zr, Cr, V each <0.25, total preferably <0.35

incidental elements and impurities, each <0.05, total <0.25,

the balance aluminium, and

having a thickness of more than 0.6 mm and in T6 temper condition having a hardness of more than 105 HB.

The increased hardness is reached by combining precipitation hardening of Mg—Si—Cu phases, Fe- and Mn-containing intermetallics and dispersoids, which are known to actually reduce the age hardening effect in balanced AlMgSi(Cu) alloys through their effect on the quench sensitivity, with a high excess of Si, which decreases the Mg solute level, to minimise the negative effect of Mn-containing dispersoids on the quench sensitivity. The supersaturation level for Mg—Si phases is not yet so high that particularly high quench sensitivities already result from the Mg-, Si-, and Cu solute content. The balanced alloy composition according to the invention is believed to combine the strength increasing effect of a silicon addition with moderate amount of copper, magnesium and manganese. It was found that this alloy provides satisfactory weldability and a hardness of at least 105 HB. It should be noted that the hardness values are expressed in the Brinell scale and were measured by a ball having a 2.5 mm diameter loaded with a mass of 62.5 kg. The hardness tests were performed according to ASTM E10 (version 2002).

In a preferred embodiment of the invention the hardness in T6 temper condition is at least 115 HB, more preferably at least 120 HB. These hardness values imply an increased machinability as well as wear resistance. The chemical composition in combination with a heat treatment ensures that adequate weldability and thus reparability is maintained: surprisingly it has been found that for Cu levels of up to 0.9% the plate alloy shows very good reparability with for instance a common 4043 filler wire.

In an embodiment the Si is in the range of 1.53-2.0%, more preferably in the range of 1.55-1.9%. It was found that this range of silicon provides a very good combination of the desirable properties, through hardening by coherent Mg—Si—Cu phases, and by primary Si, incoherent Mg₂Si and α-Al(Fe,Mn,Cu)Si intermetallic phases and dispersoids.

In an embodiment the Mn is in the range of 0.85-1.10%. It was found that this range of manganese provides a very good combination of the desirable properties, in particular by stimulating the formation of α-Al(Fe,Mn,Cu)Si intermetallic phases and dispersoids. At high Si levels, the tendency to form the relatively brittle β-AlFeSi intermetallic phase increases. However, by ensuring the presence of suitable amounts of Mn and Cu the more favourable α-Al(Fe,Mn,Cu)Si phase is stabilised.

In an embodiment the Cu is in the range of 0.5-0.7%. It was found that this range of copper provides a very good combination of the desirable properties through coherent Mg—Si—Cu phases and stabilised α-Al(Fe,Mn,Cu)Si, whilst keeping alloying cost down and ensuring good repair weldability.

In an embodiment the Zn is below 0.3%, preferably in the range of 0.17-0.3%.

In an embodiment the Fe is preferably at least 0.2%, more preferably in the range 0.2-0.5%, and even more preferably in the range 0.3-0.5% to ensure the formation of sufficient amounts of hardness increasing α-Al(Fe,Mn,Cu)Si intermetallics.

In an embodiment the Zr, Cr, V are each preferably below 0.18%, more preferably below 0.12% to further reduce the quench sensitivity.

In an embodiment the moulding plate has a machinability rating of “B” or better as defined in ‘ASM Specialty Handbook—Aluminium and Aluminium Alloys (ed. J. R. Davis), ASM International 1993, pages 328-331.

In an embodiment the moulding plate has a final thickness of 300 mm, in which the claimed hardness values can still be met in the plate centre. Preferably the final thickness is in the range of between 5 to 300 mm, more preferably in the range of between 5 to 260 mm. These thickness ranges allow the application of the moulding plate for all practical application involving moulding plate.

In an embodiment the moulding plate has been rolled to the final thickness by hot rolling only.

According to a further aspect of the invention, a method is provided of manufacturing a moulding plate comprising the subsequent (in other words “sequential”) steps of:

• • casting an ingot having a composition comprising (in weight percent):
    • Si 1.4-2.1
    • Mn 0.8-1.2
    • Cu 0.45-0.9
    • Mg 0.7-1.2
    • Ti <0.15
    • Zn <0.4
    • Fe <0.7
    • one or more of Zr, Cr, V each <0.25, total preferably <0.35
    • incidental elements and impurities, each <0.05, total <0.25, balance aluminium, and with preferred compositional ranges as set out in the description hereinabove.
  • homogenising and/or preheating the ingot,
  • working said plate to a final thickness, preferably by hot rolling and/or cold rolling, more preferably by hot rolling only,
  • subjecting to heat treatment comprising solution heat treating followed by rapid cooling,
  • ageing,
  • wherein the cooling rate during said rapid cooling is chosen so as to obtain a hardness of the moulding plate of at least 105 HB.

By manufacturing a moulding plate according to the invention a high hardness product with a high content of chip-breaking intermetallics is obtained. The cooling rate during the rapid cooling after solution heat treating is important because this cooling rate determines the amount of solute content of Mg, Si and Cu which were dissolved during the solution heat treatment.

In an embodiment of the invention the heat treatment after hot rolling or hot pressing is a T6-treatment.

In an embodiment the homogenisation temperature is at least 450° C., preferably at least 500° C., more preferably between 500 and 595° C., preferably for between 1 to 25 hours, more preferably for between 10 to 16 hours. The pre-heat temperature is at least 570° C., between about 300° C. and 570° C., preferably between 350 and 530° C., preferably for between 1 to 25 hours, more preferably for between 1 and 10 hours.

In an embodiment the solution heat-treating temperature is at least 500° C., preferably at least 520° C. and more preferably at least 540° C. In an embodiment the cooling rate after solution heat-treating from the solution heat-treating temperature to below 250° C., preferably to below 150° C. and more preferably to below 100° C., is at least 1° C./s, preferably at least 2° C./s more preferably 5° C./s, even more preferably at least 10° C./s. It should be noted that the cooling rate of the product during quenching is dependent on the location within the product. The centre of the product cools down more slowly than the surface of the product. Consequently, since the final hardness is dependent on the cooling rate, the hardness will be lower if the local cooling rate during quenching is lower. The critical point in the product is defined as the point where the cooling rate during quenching is the lowest. The abovementioned cooling rates relate to the cooling rate at the critical point.

In a further embodiment, the ageing process comprises natural ageing for a maximum duration of 28 days, preferably for a maximum duration of 14 days, more preferably for a maximum duration of 7 days, even more preferably for a maximum duration of 2 days, followed by an artificial ageing treatment equivalent to ageing at about 180 to 200° C. for about 1-10 hours. It is known to the skilled person that time and temperature of an annealing are usually not chosen independently. The ageing process is thermally activated, resulting in the situation that a high temperature coupled with a short time is equivalent to a lower temperature and a longer time, i.e. the same metallurgical state is reached after the ageing treatment.

In an embodiment of the invention the working step comprises a rolling or pressing step. In a further embodiment the rolling step comprises a hot rolling and/or a hot pressing step and/or cold-rolling step. Preferably, the working step comprises hot rolling and/or hot pressing only.

In an embodiment of the invention the casting step is a near-net shape casting step, wherein the dimensions of the cast product approximates the final product.

A particular embodiment of the invention will now be explained by the following non-limitative examples and figure. It should be noted that the chemical composition of the alloys was varied by mixing cuttings of a brazing alloy, consisting mostly of an AA3000-series core alloy clad with a Si-rich AA4000-series alloy with technical purity Al 99.0 after which Cu and/or Mg and/or other elements can be added to obtain the final chemistry.

TABLE 1
Average composition of tested alloys and hardness in T6-condition.
									content brazing
Alloy	Si	Fe	Cu	Mn	Mg	Zn	Ti	HB	alloy (%)
Al 99.0	0.4	0.6	0.03	0.03	0.03	0.07	—	—	0
Brazing alloy	2.0	0.4	0.5	1.0	0.40	0.25	0.05	—	100
Example 1	1.72	0.37	0.61	0.77	0.97	0.21	0.05	124	82
Example 2	1.70	0.39	0.91	0.95	0.85	0.21	0.05	124	81
Example 3	2.10	0.38	0.50	1.03	0.88	0.25	0.05	124	100
Example 4	1.68	0.41	0.40	0.78	0.98	0.21	0.05	123	80
Example 5	1.71	0.43	0.51	0.76	0.70	0.21	0.05	122	82
Example 6	1.59	0.38	0.61	0.81	0.98	0.10	0.03	123	75
Example 7	1.60	0.39	0.64	0.95	0.91	0.02	0.05		80

These alloys were homogenised at a temperature above 510° C., optionally hot rolled, solution heat treated at 550° C., cooled down with at least 10° C./s to maximise the solute content of Mg, Si and Cu, stored for 14 days at room temperature, and aged following an ageing treatment equivalent to 190° C. for 2-6 hours. In this way, a high-hardness T6-temper product with a high content of chip-breaking intermetallics is obtained, leading to a hardness of at least 120 HB. Example 7 was solution heat treated at 530° C. and stored at room temperature for a period of 1 day, the remainder of the process conditions being as given above for the other alloys.

The hardness profiles of plates with the composition according to Example 7 with thicknesses of 80, 100 or 150 mm are shown in FIG. 1. Along the X-axis the distance (L) to the centre of the plate in the thickness direction in mm is given, and along the Y-axis the hardness in HB values is given at different locations over the thickness of the plate. All measured values show a hardness value of at least 120 HB at every location over the thickness of the plate.

It is of course to be understood that the present invention is not limited to the described embodiments and examples described above, but encompasses any and all embodiments within the scope of the description and the following claims.

Claims

1. Moulding plate of an aluminium wrought alloy comprising, in weight percent:

Si 1.4-2.1

Mn 0.8-1.2

Cu 0.45-0.9

Mg 0.7-1.2

Ti <0.15

Zn <0.4

Fe <0.7

one or more of Zr, Cr, V each <0.25

incidental elements and impurities, each <0.05, total <0.25,

the balance aluminium, and

having a thickness of more than 0.6 mm and in T6 temper condition having a hardness of more than 105 HB.

2. Moulding plate according to claim 1, wherein Si is in the range of 1.53-2.0%.

3. Moulding plate according to claim 1, wherein Si is in the range of 1.55-1.9%.

4. Moulding plate according to claim 1, wherein Mn is in the range of 0.85-1.10%.

5. Moulding plate according to claim 1, wherein Cu is in the range of 0.5-0.7%.

6. Moulding plate according to claim 1, wherein Mg is in the range of 0.9-1.1%.

7. Moulding plate according to claim 1, wherein Zn is below 0.3%.

8. Moulding plate according to claim 1, wherein Zn is in the range of 0.17-0.3%.

9. Moulding plate according to claim 1, wherein the moulding plate has a machinability rating of “B” or better.

10. Moulding plate according to claim 1, wherein the moulding plate has a final thickness in the range of 5 to 300 mm.

11. Moulding plate according to claim 1, wherein the moulding plate has a final thickness in the range of 5 to 260 mm.

12. Moulding plate according to claim 1, wherein the moulding plate has been rolled to the final thickness by hot rolling only.

13. Moulding plate according to claim 1, having a hardness of more than 115 HB.

14. Moulding plate according to claim 1, having a hardness of more than 120 HB.

15. Method of manufacturing a moulding plate comprising the sequential steps of:

casting a composition comprising (in weight percent): Si 1.4-2.1 Mn 0.8-1.2 Cu 0.45-0.9 Mg 0.7-1.2 Ti <0.15 Zn <0.4 Fe <0.7 one or more of Zr, Cr, V each <0.25 incidental elements and impurities, each <0.05, total <0.25, balance aluminium,

homogenising and preheating the cast composition,

working the homogenized and preheated cast composition to form said plate to a final thickness,

subjecting said plate to heat treatment comprising solution heat treating followed by rapid cooling,

ageing said plate,

wherein the cooling rate during said rapid cooling is chosen to obtain a hardness of the moulding plate of at least 105 HB.