An Al-Mg Alloy Wire FIELD OF THE INVENTION The present invention relates to an Al-Mg alloy wire, which is applied to braid wires of coaxial cables, braid wires of various pressure pipes and Aluminum welding wires, and which belongs to aluminum metallurgy field. BACKGROUND OF THE INVENTION At present, an Al-Mg alloy wire, which is used in braid wires of coaxial cables, braid wires of various pressure pipes and Aluminum welding wires manufactured by most factories in China, has a formulation comprising Mg, Mn, Cr and Al, the best quality of which is not achieved, and thus the product is prone to curling, be oxidized, and be scratched and has an unsatisfying tensile strength (the strength of hard wire is about 260MPa), bad finish and tends to break under a high speed mechanical process, which affects product quantity seriously. As result, such an Al-Mg alloy wire can not meet requirements of clients and the domestic and oversea market. SUMMARY OF THE INVENTION With respect to the above mentioned technical problems, an object of the present invention is to provide an Al-Mg alloy wire with good quality and low cost. A technical solution of the present invention is achieved by an Al-Mg alloy wire being composed of (in wt%): Mn 0.01-0.30%, Ti 0.05-0.35%, Cr 0.03-0.42%, Mg 2-8%, and the balance being Al, excluding copper or zinc. Preferably, the Al-Mg alloy wire is composed of (in wt%): Mn 0.05-0.25%, Ti 0.06 0.25%, Cr 0.08-0.4%, Mg 3-7%, and the balance being Al. Most preferably, the Al-Mg alloy wire is composed of (in wt%): Mn 0.08-0.23%, Ti 0.07-0.24%, Cr 0.1-0.35%, Mg 3.3-6.5%, Fe 0.01-0.20%, Si 0.03-0.25%, Ni 0.02-0.15%, Ga 0.01-0.25%, and the balance being Al. In the present invention, Mn increases strength and refines molten Al; Ti 1 increases flexibility, inhibits oxidation and refines the melted aluminum liquid; Cr and Mg increase finish and strength, Fe, Si and Ni meet the requirement of mechanical property in the process. The Al-Mg alloy wire according to the present invention has advantages as follows: a phenomenon that a conventional Al-Mg alloy wire is prone to be oxidized is eliminated, the tensile strength is improved (the strength of hard wire is about 400MPa), the wire does not curl, may not be scratched, and has resistance to oxidation and excellent finish. Therefore, it has good quality and low cost characteristics. In the present invention, Aluminum, as a raw material, is an aluminum product obtained from Alcan Ningxia Aluminum Company Limited, other metallic raw materials are commercially available from China National Nonferrous Metals Industry Eastern Supply Marketing Corporation. DETAILED DESCRIPTION OF THE INVENTION Example 1: An Al-Mg alloy wire is composed of (in wt%): Mn 0.05%, Ti 0.12%, Cr 0.16%, Mg 4.5%, and Al 95.17%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 0.5 kg of Mn, 1.2 kg of Ti and 1.6 kg of Cr are melted, and then 4.95 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 8.25 kg, is cast and formed for serving. (2) In a smelting furnace, 946.75 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 45 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are 2 put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 2: An Al-Mg alloy wire is composed of (in wt%): Mn 0.12%, Ti 0.17%, Cr 0.09%, Mg 5%, and Al 94.62%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.2 kg of Mn, 1.7 kg of Ti and 0.9 kg of Cr are melted, and then 5.7 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 9.5 kg, is cast and formed for serving. (2) In a smelting furnace, 940.5 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 50 kg of Mg is added. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (the temperature of which is controlled at 670'C±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 3: An Al-Mg alloy wire is composed of (in wt%): Mn 0.22%, Ti 0.09%, Cr 0.13%, Mg 3.8%, and Al 95.76%. 3 A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 2.2 kg of Mn, 0.9 kg of Ti and 1.3 kg of Cr are melted, and then 6.6 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 11 kg, is cast and formed for serving. (2) In a smelting furnace, 951 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 38 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 4: An Al-Mg alloy wire is composed of (in wt%): Mn 0.07%, Ti 0.25%, Cr 0.07%, Mg 6.3% and Al 93.31%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 0.7 kg of Mn, 2.5 kg of Ti and 0.7 kg of Cr are melted, and then 5.85 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 9.75 kg, is cast and formed for serving. (2) In a smelting furnace, 927.25 kg of aluminum as raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 63 kg of Mg is added into the smelting furnace. After 4 the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 5: An Al-Mg alloy wire is composed of (in wt%): Mn 0.20%, Ti 0.08%, Cr 0.32%, Mg 3.1%, Fe 0.06%, and Al 96.24%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 2 kg of Mn, 0.8 kg of Ti, 3.2 kg of Cr and 0.6 kg of Fe are melted, and then 9.9 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 16.5 kg, is cast and formed for serving. (2) In a smelting furnace, 952.5 kg of aluminum as raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 31 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ± 10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 6: An Al-Mg alloy wire is composed of (in wt%): Mn 0.11%, Ti 0.15%, Cr 0.28%, Mg 5 4.7%, Si 0.13%, and Al 94.63%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.1 kg of Mn, 1.5 kg of Ti, 2.8 kg of Cr and 1.3 kg of Si are melted, and then 10.05 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 16.75 kg, is cast and formed for serving. (2) In a smelting furnace, 936.25 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 47 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 7: An Al-Mg alloy wire is composed of (in wt%): Mn 0.06%, Ti 0.23%, Cr 0.21%, Mg 5.9%, Ni 0.14%, and Al 93.46%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 0.6 kg of Mn, 2.3 kg of Ti, 2.1 kg of Cr and 1.4 kg of Ni are melted, and then 9.6 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 16 kg, is cast and formed for serving. (2) In a smelting furnace, 925 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum 6 alloy ingot is melted completely, 59 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 8: An Al-Mg alloy wire is composed of (in wt%): Mn 0.17%, Ti 0.20%, Cr 0.15%, Mg 5.3%, Ga 0.21%, and Al 93.97%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.7 kg of Mn, 2 kg of Ti, 1.5 kg of Cr and 2.1 kg of Ga are melted, and then 10.95 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 18.25 kg, is cast and formed for serving. (2) In a smelting furnace, 928.75 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±1 oC. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 53 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 9: 7 An Al-Mg alloy wire is composed of (in wt%): Mn 0.26%, Ti 0.18%, Cr 0.25%, Mg 6.9%, Fe 0.14%, and Al 92.27%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 2.6 kg of Mn, 1.8 kg of Ti, 2.5 kg of Cr and 1.4 kg of Fe are melted, and then 12.45 kg of an aluminum ingot is added, and thus an aluminum alloy ingot, which weights 20.75 kg, is cast and formed for serving. (2) In a smelting furnace, 910.25 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ± i10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 69 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled at 670C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 10: An Al-Mg alloy wire is composed of (in wt%): Mn 0.14%, Ti 0.30%, Cr 0.10%, Mg 6%, Si 0.15%, and Al 93.31%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.4 kg of Mn, 3 kg of Ti, 1 kg of Cr and 1.5 kg of Si are melted, and then 10.35 kg of an aluminum ingot is added, and thus an aluminum alloy ingot, which weights 17.25 kg, is cast and formed for serving. (2) In a smelting furnace, 922.75 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700C ±10'C. Then, the aluminum alloy ingot is added into 8 the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 60 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 11: An Al-Mg alloy wire is composed of (in wt%): Mn 0.12%, Ti 0.15%, Cr 0.25%, Mg 4.5%, Fe 0.05%, Si 0.08%, Ni 0.06%, Ga 0.03%, and Al 94.76%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.2 kg of Mn, 1.5kg of Ti, 2.5kg of Cr, 0.5kg of Fe, 0.8 kg of Si, 0.6kg of Ni and 0.3kg of Ga are melted, and then 11.1 kg of an aluminum ingot is added, and thus an aluminum alloy ingot, which weights 18.5 kg, is cast and formed for serving. (2) In a smelting furnace, 936.5 kg of aluminum as raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 45 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be 9 drawn to form Al-Mg alloy wires having various specifications. Example 12: An Al-Mg alloy wire is composed of (in wt%): Mn 0.18%, Ti 0.12%, Cr 0.32%, Mg 3.8%, Fe 0.12%, Si 0.09%, Ni 0.04%, Ga 0.05%, and Al 95.28%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.8 kg of Mn, 1.2 kg of Ti, 3.2 kg of Cr, 1.2 kg of Fe, 0.9 kg of Si, 0.4 kg of Ni and 0.5 kg of Ga are melted, and then 13.8 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 23 kg, is cast and formed for serving. (2) In a smelting furnace, 939 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 38 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 13: An Al-Mg alloy wire is composed of (in wt%): Mn 0.15%, Ti 0.21%, Cr 0.21%, Mg 5.6%, Fe 0.09%, Si 0.14%, Ni 0.12%, Ga 0.18%, and Al 93.3%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.5 kg of Mn, 2.1 kg of Ti, 2.1 kg of Cr, 0.9 kg of Fe, 1.4 kg 10 of Si, 1.2 kg of Ni and 1.8 kg of Ga are melted, and then 16.5 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 27.5 kg, is cast and formed for serving. (2) In a smelting furnace, 916.5 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 56 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 14: An Al-Mg alloy wire is composed of (in wt%): Mn 0.09%, Ti 0.14%, Cr 0.14%, Mg 4.9%, Fe 0.15%, Si 0.18 %, Ni 0.08%, Ga 0.15%, and Al 94.17%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 0.9 kg of Mn, 1.4 kg of Ti, 1.4 kg of Cr, 1.5 kg of Fe, 1.8 kg of Si, 0.8 kg of Ni and 1.5 kg of Ga are melted, and then 13.95 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 23.25 kg, is cast and formed for serving. (2) In a smelting furnace, 927.75 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ± i1 0C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 49 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are 11 put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 15: An Al-Mg alloy wire is composed of (in wt%): Mn 0.13%, Ti 0.08%, Cr 0.19%, Mg 5.2%, Fe 0.18%, Si 0.05%, Ni 0.09%, Ga 0.09%, and Al 93.99%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.3 kg of Mn, 0.8 kg of Ti, 1.9 kg of Cr, 1.8 kg of Fe, 0.5 kg of Si, 0.9 kg of Ni and 0.9 kg of Ga are melted, and then 12.15 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 20.25 kg, is cast and formed for serving. (2) In a smelting furnace, 927.75 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±1 0'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 52 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 16: An Al-Mg alloy wire is composed of (in wt%): Mn 0.20%, Ti 0.17%, Cr 0.17%, Mg 12 5.5%, Fe 0.10%, Si 0.16 %, Ni 0.10%, Ga 0.04%, and Al 93.56%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 2 kg of Mn, 1.7 kg of Ti, 1.7 kg of Cr, 1 kg of Fe, 1.6 kg of Si, 1 kg of Ni and 0.4 kg of Ga are melted, and then 14.1 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 23.5 kg, is cast and formed for serving. (2) In a smelting furnace, 921.5 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely,55 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding furnace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 17: An Al-Mg alloy wire is composed of (in wt%): Mn 0.17%, Ti 0.20%, Cr 0.23%, Mg 6.2%, Fe 0.07%, Si 0.23 %, Ni 0.07%, Ga 0.14%, and Al 92.69%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.7 kg of Mn, 2 kg of Ti, 2.3 kg of Cr, 0.7 kg of Fe, 2.3 kg of Si, 0.7 kg of Ni and 1.4 kg of Ga are melted, and then 16.65 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 27.75 kg, is cast and formed for serving. (2) In a smelting furnace, 910.25 kg of aluminum as a raw material is melted for 3 13 hours at a temperature of 700'C±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 62 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 18: An Al-Mg alloy wire is composed of (in wt%): Mn 0.22%, Ti 0.18%, Cr 0.28%, Mg 5.7%, Fe 0.13%, Si 0.20 %, Ni 0.05%, Ga 0.20%, and Al 93.04%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 2.2 kg of Mn, 1.8 kg of Ti, 2.8 kg of Cr, 1.3 kg of Fe, 2 kg of Si, 0.5 kg of Ni and 2 kg of Ga are melted, and then 18.9 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 31.5 kg, is cast and formed for serving. (2) In a smelting furnace, 911.5 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10"C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 57 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled 14 at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 19: An Al-Mg alloy wire is composed of (in wt%): Mn 0.16%, Ti 0.09%, Cr 0.12%, Mg 5%, Fe 0.17%, Si 0.15%, Ni 0.13%, Ga 0.16%, and Al 94.02%. A production process of the present invention is as follows (based on 1, 000 kg for example): (1) In a small stove, 1.6 kg of Mn, 0.9 kg of Ti, 1.2 kg of Cr, 1.7 kg of Fe, 1.5 kg of Si, 1.3 kg of Ni and 1.6 kg of Ga are melted, and then 14.7 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 24.5 kg, is cast and formed for serving. (2) In a smelting furnace, 925.5 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700'C ±10'C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 50 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled at 670'C ±10'C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. Example 20: An Al-Mg alloy wire is composed of (in wt%): Mn 0.08%, Ti 0.13%, Cr 0.26%, Mg 6%, Fe 0.06%, Si 0.10%, Ni 0.11%, Ga 0.07%, and Al 93.19%. A production process of the present invention is as follows (based on 1, 000 kg for example): 15 (1) In small stove, 0.8 kg of Mn, 1.3 kg of Ti, 2.6 kg of Cr, 0.6 kg of Fe, 1 kg of Si, 1.1 kg of Ni and 0.7 kg of Ga are melted, and then 12.15 kg of an aluminum ingot is added, thus an aluminum alloy ingot, which weights 20.25 kg, is cast and formed for serving. (2) In a smelting furnace, 919.75 kg of aluminum as a raw material is melted for 3 hours at a temperature of 700*C ±10*C. Then, the aluminum alloy ingot is added into the melted aluminum as the raw material in the smelting furnace. After the aluminum alloy ingot is melted completely, 60 kg of Mg is further added into the smelting furnace. After the Mg is melted completely, 10 kg of ammonium chloride and 1 kg of borax are put into the smelting furnace and practiced to form a slag for the above melted metallic liquid contained aluminum, and then a slag removal procedure is performed. Finally, the above melted metallic liquid, which has been subjected to the slag removal procedure, is fed into a holding fumace (a temperature of which is controlled at 6700C±10C) and further dragged out to form an Al-Mg alloy rod, which may be drawn to form Al-Mg alloy wires having various specifications. The comparison of the performance between the Al-Mg alloy wire according to the present invention and a conventional one is as follows: Name of a product specification tensile strength resistivity (PMA) (Q mm/m) The Al-Mg alloy wire according to 0 0.16 400-420 s 0.05945 the present invention A conventional Al-Mg alloy wire 0 0.16 260-280 s 0.06525 As can be seen from the above table, each performance of the Al-Mg alloy wire according to the present invention excesses significantly over that of the conventional one, which shows that the Al-Mg alloy wire according to the present invention has incomparable advantage over the conventional Al-Mg alloy wire. 16/1 Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirely by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application, or patent cited in this text is not repeated in this text is merely for reasons of conciseness. Reference to cited material or information contained in the text should not be understood as a concession that the material or information was part of the common general knowledge or was known in Australia or any other country. The discussion of the background art is included exclusively for the purpose of providing a context for the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was common general knowledge in the field relevant to the present invention in Australia or elsewhere before the priority date. 16/2