FIELD OF THE INVENTION The present invention relates to a free-machining wrought AIMgSi-alloy product for machining or free-cutting applications. The invention further relates to a process for producing such free-machining wrought AIMgSi-alloy products. BACKGROUND OF THE INVENTION The alloy and alloy tempers used herein are in accordance with the well-known aluminium alloy product standards of the Aluminium Association. All percentages are in weight percents, unless otherwise indicated. An extruded bar is solid product that is long in relation to cross section, which is square or rectangular (exploding plate and flattened wire) with sharp or rounded corners or edges, or is regular hexagon or octagon, and in which at least one perpendicular distance between parallel faces is over 10 mm. An extruded rod is a solid product over 10 mm in diameter that is long in relation to cross section. Alloys for free-machining applications and also known as free-machining alloy products need to have good machinability properties. Machinability can be defined as the relative ease (or difficulty) of removing metal in transforming a workpiece into a finished product. The criteria for machinability may change depending on the specific machining operation and the product details. One of the most important characteristics of the machinability of aluminium is the break up of the formed chips. If the chips do not break long chips may be formed which can lead to a wide range of problems ranging from products that are out of specification to problems with the extraction of chips from the machine. Traditional alloys for machining applications such as AA6061 and AA6082 have relatively poor chip fracture performance. To improve this performance elements such as lead, tin, indium and bismuth are added as they form soft phases with relatively low melting temperatures. During the formation of the chip these soft phases form a weakness in the material at which the chip may break. It has also been suggested that with sufficient temperature and pressure at the cutting zone that the soft phase acts as a lubricant. These two mechanisms result in small chips and an improved surface finish of the machined part. A typical alloy for free-machining applications which contains elements to form phases with relatively low melting temperatures is AA6262, which contains purposive additions of lead and bismuth. However, due to environmental and health concerns, for the future it is envisaged that lead will be banned from aluminium alloys whilst bismuth is a relative expensive alloying element. The chemical compositions in weight percent of known standard alloys AA6061 , AA6082 and AA6262 for machining applications are set out below. Single numbers indicate maxima and the balance is aluminium with a total of up to 0 15 unspecified impurity elements.

SUMMARY OF THE INVENTION An object of the present invention is to provide a free-machining wrought alloy product devoid of any low melting phases, in particular of one or more of Pb, Bi, Sn, Cd and In, suitable for free-machining applications. An object of the invention is to provide a free-machining wrought alloy product with improved machining performance in comparison with alloys according to standard AA6061 or standard AA6082. A further object of the invention is to provide a free-machining wrought alloy product with a machining performance close to that of standard AA6262. One or more of these objects of the invention are achieved by a free-machining wrought Al-Mg-Si alloy product, preferably in the form of an extruded product, characterised in that it contains, in weight %: Si 0.6-2.0, Fe 0.2-1.0, Mg 0 5-2 0, Cu max. 1.0, Mn max. 1.5, Zn max. 1.0, Cr max 0.35, Ti max. 0.35, Zr 0.04-0.3, impurities each max 0.05, total max. 0.15, Aluminium balance. The free-machining wrought aluminium alloy of the invention does not contain lead or expensive alloying elements such as bismuth, tin, cadmium or indium. The alloy product of the invention has improved machinability performance in comparison to the standard alloys products, which do not contain elements, which form soft phases with relatively low melting temperatures. The alloy product of the present invention also avoids potential costs for extraction systems, separate chip recycling etc if in the future elements such as indium, tin, cadmium or bismuth are restricted, as has been the case with lead. The alloy product according to the invention is free from each of the elements selected from the group of Pb, Bi, Sn, Cd and In. In practical terms this would mean that the content for each of these elements is <0.05%, and preferably <0.02%, and more preferably the alloy product is essentially free or substantially free from these elements. With "substantially free" and "essentially free" we mean for this invention that no purposeful addition of this alloying element was made to the composition, but that due to impurities and/or leaching from contact with manufacturing equipment, trace quantities of this element may, nevertheless, find their way into the final alloy product. The wrought alloy product contains a relatively large amount of precipitation forming elements or intermetallic compounds which form a mixture of a high number of brittle particles which can act as stress raisers and crack initiation sites. As a result chips will fracture more easily. The increased precipitation strengthening also reduces the toughness of the material, which also assists chip fracture. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The wrought alloy product has an Si content of 0.6-2.0 wt % to increase the strength, the hardness of the alloy product and to increase the amount of Si-containing intermetallic particles which together improves the machinability as the chips will shear off and break more easily. High amounts of silicon can however result in significant abrasive tool wear and can also result in the chips being torn from the surface of the workpiece during machining which results in the formation of undesirable burrs. The Si content may be in the range 0.6-1.45 wt.%, and preferably in the range 0.6-1.35 wt.% or may be in the range 0.9-2.0 wt.%, and more preferably in the range 1.0-2.0 wt.%. The wrought alloy product has a Fe content of 0.2-1.0 wt.%, which forms a relatively soft intermetallic with aluminium which acts as a chip breaker without giving a significant increase in tool wear. However iron also forms some hard intermetallics with other elements which increase tool wear. A too high iron content is therefore not desirable. The Fe content may be in the range 0.35-1.0 wt.% or alternatively may be in the range 0.35- 0.8 wt.%. The Mg content of the wrought alloy product is 0.5-2.0 wt.%. The presence of Mg increases the strength of the alloy and increases the amount of Mg-containing intermetallic particles, which further improves the machinability as the chips will shear off and break more easily. The friction between the tool and the workpiece is reduced during machining and the chips curl tighter and break up more easily. The Mg content may be 0.75-2.0, and preferably 0.85-2.0, and more preferably 1.0-2.0 wt.%. Copper also increases the strength of the alloy product. In the present invention Si and Mg are also present which results in the increase in strength being combined with a reduction in the toughness of the alloy, which improves the shape of the chips. In the present invention there is maximum 1.0 wt.% of copper present. The Cu content may be maximum 0.7 wt.% or preferably maximum 0.40 wt % or more preferably maximum 0.35 wt.%. The Cu content may be in the range is 0.15 to 1.0 wt.%. Manganese forms hard intermetallic phases with other elements, which act as chip breakers. Man also forms fine dispersions which increase the strength of the alloy. The alloy of the present invention contains maximum 1.5 wt.% Mn. The Mn content may be 0.45-1.5 wt.%, and preferably 0.6-1.3 wt.%. Chromium also may form hard intermetallic phases with other elements which have limited effectiveness as chip breakers and chromium also forms fine dispersoids, which increase the strength of the alloy. The wrought alloy product of the present invention contains maximum 0.35 wt.% chromium. The Cr content may be maximum 0.2 wt.%, and preferably maximum 0.1 wt.%, and more preferably maximum 0.05 wt.%. The wrought alloy product has a Zn content of max 1.0 wt%. In particular in combination with Mg, Zn increases both the strength of the alloy product and improves chip shape. In addition the addition of Zn compensates the corrosion potential of the Cu present in the alloy product. The Zn content may be 0.1-1.0 wt.%, and preferably 0.2-1.0 wt.%, and more preferably 0.3- 1.0 wt.%. The Zn content may be maximum 0.6 wt.%. Titanium is added as a grain refiner of the as-cast microstructure and can be present up to a maximum of 0.35 wt.%, and preferably up to 0.15 wt.%. As known in the art of grain refining aluminium wrought alloys, the Ti can be added in conjunction with or as TiB and/or TiC. Zirconium is an important alloying element in the product according to the invention and forms relatively hard intermetallic phases with other elements, which act as chip breakers. Furthermore, the presence of Zr in the defined range surprises grain growth during heat treatments. The wrought alloy product of the present invention contains up to 0.3 wt.%, and preferably 0.04-0.3 wt.%, and more preferably 0.07-0.3 wt.%. In an embodiment the alloy product according to the invention is free from Ni. In practical terms this would mean that the content is <0.02 wt.%, and preferably <0.01 wt.%, and more preferably the alloy product is substantially free from Ni. In a preferred embodiment the free-machining wrought aluminium alloys according to this invention is in the form of an extruded rod or bar, whereby "rod" and "bar" are defined according to the AA nomenclature. The free-machining wrought aluminium alloy product of the present invention has more preferably a recrystallised microstructure meaning that at least 80% or more, and preferably 90% or more of the grains in the final temper, for example a T2, T3, T5, T6, e.g. T651 , T651 1 , T8 or T9 temper, are recrystallised. It has been found that the recrystallised grain structures in combination with the relatively large amount of intermetallic particular in the alloy product considerably further improves the chip breaking effect in the alloy product according to the invention. A T2 temper conventionally applies to products that have been cooled from an elevated- temperature shaping process, cold worked, and naturally aged to a substantially stable condition. A T3 temper conventionally applies to products that have been solution heat treated, cold worked, and naturally aged to a substantially stable condition. A T5 temper conventionally applies to products that have been cooled from an elevated-temperature shaping process and then artificially aged. A T6 temper conventionally applies to products that have been solution heat treated and then artificially aged. A T8 temper conventionally applies to products that have been solution heat treated, cold worked, and then artificially aged. Whereas a T9 temper conventionally applies to products that are solution heat- treated, artificially aged, and then cold worked. In another aspect the present invention relates to a process for producing the free- machining AIMgSi alloy product containing in weight %: Si 0.6-2.0, Fe 0.2-1.0, Mg 0.5-2.0, Cu max. 1.0, Mn max. 1.5, Zn max. 1.0, Cr max. 0.35, Ti max. 0.35, Zr max. 0.3, preferably Zr 0.04-0.3, impurities max. 0.05 each, total max. 0.15, Aluminium balance, and comprising the steps of: (i) homogenising a cast billet of defined composition at a temperature in the range of 420 to 52O0C, preferably 450 to 5100C; (ii) extruding the alloy into a product, (iii) solution heat treating ("SHT") at a temperature above 5000C of the cold worked alloy product followed by a quench, and whereby SHT can be done by friction heat at the die during extrusion or after extrusion in a separate heat treatment furnace, (iv) ageing the SHT alloy product to a final temper, and wherein the alloy product has preferably in its final temper a recrystallised microstructure. It has surprisingly been found that this process in combination with an alloy of the given composition results in improved machining performance in comparison with using standard T2, T3, T5, T6, T8 or T9 processing routes. In an embodiment of the process according to the invention the extruded product is cold worked prior solution heat treatment. In another embodiment of the process according to the invention the extruded product is being cold worked after the solution heat treatment. This cold working can be done either before or after ageing, depending on the desired temper. In a preferred embodiment of the process according to the invention the extruded product is being cold worked both before and after the solution heat treatment. In all these three embodiments the cold working step assist in recrystallising the microstructure of the alloy product, which further improves chip breaking. In all three embodiments incorporating the cold working operation, the cold working operation is preferably carried out by a drawing or stretching operation such that the length of the alloy product is extended by 1 to 30% during such operation, and preferably by 2 to 18%. Particularly good results have been obtained when cold working operation before SHT is a larger drawing step than the cold working operation after SHT. In a further aspect the present invention also relates to a free-machining wrought aluminium alloy product containing, in weight %: Si 0.6-2.0, Fe 0.2-1.0, Mg 0.5-2.0, Cu max. 1.0, Mn max. 1.5, Zn max. 1.0, Cr max. 0.35, Ti max. 0.35, Zr max. 0.3, preferably Zr 0.04-0.3, impurities max. 0.05 each, total max. 0.15, aluminium balance, and preferred ranges for the elements have been set out above, and produced by a method comprising the steps of: (i) homogenising a cast billet of defined composition at a temperature in the range of 420 to 5200C, preferably 450 to 51O0C, (ii) extruding the alloy, (iii) solution heat treating ("SHT") the alloy at a temperature above 5000C followed by a quench, and whereby SHT can be done by friction heat at the die during extrusion or after extrusion in a separate heat treatment furnace, (iv) ageing the alloy, and wherein the alloy product has in its final temper preferably a recrystallised microstructure. An alloy of the given composition produced by the given method has improved machining performance in comparison with an alloy of the given composition produced following T2, T3, T5, T6, T8 or T9 processing routes. In an embodiment of this product to the invention the extruded product is also cold worked prior solution heat treatment. In another embodiment of the product according to the invention the extruded product is being cold worked after the solution heat treatment. This cold working can be done either before or after ageing, depending on the desired temper. In a preferred embodiment of the product according to the invention the extruded product is being cold worked both before and after the solution heat treatment. In all three embodiments the cold working operation is preferably carried out by a drawing or stretching operation such that the length of the alloy product is extended by 1 to 30% during such operation, and preferably by 2 to 18%. Particularly good results have been obtained when cold working operation before SHT is a larger drawing step than the cold working operation after SHT. EXAMPLE The invention is now described with reference to some examples, which do not limit the scope of the invention.

Table 1. Chemical composition of the 5 alloys tested, all percentages are by weight, and balance is aluminium.

Table 1 shows the compositions of alloys 1 and 2 in accordance with the present invention and three alloys according to standard AA6061 , AA6082 and AA6262 respectively. The alloys of Table 1 have been press quenched and further processed according to standard processing into T8 and T9 conditions, and an alternative modified T8 processing route hereinafter referred to as P1 comprising: homogenisation at a temperature of 4800C for 12 hours, - extrusion of the homogenised product, air-cooling after extruding, cold working of the extruded and cooled product by means of a first drawing step extending the product by 12%, a solution heat treatment for 30 minutes at 53O0C with water quench, - cold working of the solution heat treated and quenched product in a second drawing step extending the product by 3%, and an ageing treatment for 5 hours at 18O0C. The free-machining performance of each of the alloys after each processing route was then analysed and the results obtained are summarised in Table 2. The free-machinability rating was determined using a machining test and which allows for a relative comparison with another alloy tested under the same conditions. The results were used to define in particular the relative chip shape and size relative to the typical performance of AA6262 in turning and forming operations. The values are normalised to give approximately 1 for conventional lead-containing AA6262 in the standard T9 condition. The machining test is carried out rods having a diameter of 25 mm and using water- soluble oil emulsion, viz. a mixture of water with 7% of Castrol-Hysol R (trade mark), being a commercially available oil. The different criteria are: (i) rough turning, e.g. chip shape and chip length, (ii) fine turning, e.g. chip shape and tearing on edges, and (iii) forming, e.g. chip length, chip shape and tearing of edges. Weight factors are given to each criteria and which allow to make a relative machinability rating. From the results of Table 2 it can be seen that each of alloy 1 and 2 according to the invention have a better free-machinability rating than standard AA6061 and AA6082 in a similar temper, e.g. by comparing alloy 2 in T8 temper against AA6061 in the T8 temper. Furthermore it can be seen that alloy 2 has a better free-machinability rating than alloy 1 in a similar temper, e.g. by comparing alloy 2 in T9 temper against alloy 1 in the T9 temper. Most likely this improvement is due to the addition of the alloying elements Cu and Zn which greatly improve chip shape. Table 2.

The process P1 according to the invention further enhances the free-machinability rating of the alloys tested, such that alloy 2 has almost similar rating as the lead- containing AA6262 alloy, but without all the disadvantages associated with the addition of lead, bismuth and/or tin as a mandatory alloying element. The advantage of the process according to the invention is believed to be the lower homogenisation temperature (420- 52O0C) compared to standard homogenisation practice (540-5800C) for this type of AAΘxxx-series alloys, and which is preferably carried out in combination with a cold working step, e.g. by means of a drawing operation, prior to SHT. This leads to the presence of a high amount intermetallic particulars in a recrystallised grain structure, which is believed to improve chip shape. The results of these machinability tests have been confirmed on material in industrial scale trials. Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as hereon described.