Method for producing a solidified lightweight aluminium or magnesium alloy

Abstract

A lightweight aluminium or magnesium alloy comprises aluminium or magnesium and one or more alloying elements, including dispersoid forming elements increasing the liquidus temperature of the alloy. The alloy is ejected in a molten state from at least one nozzle and is rapidly solidified. The lightweight alloy is produced from at least one lightweight metal based composition that comprises predominantly aluminium or magnesium. This composition is heated, in a first heating step, to a first temperature that is lower than the liquidus temperature of the alloy to produce a melt of the lightweight metal based composition that is supplied through a piping to the nozzle. In the piping, the lightweight alloy melt is heated to have a second temperature that is preferably higher than the liquidus temperature of the alloy. The first temperature reduces the tendency of magnesium to oxidize whilst the second temperature dissolves all of the alloying elements.

1 . A method for producing a solidified lightweight alloy based on aluminium or magnesium as lightweight metal, wherein the lightweight alloy has a liquidus temperature and a solidus temperature, and a predetermined difference between the liquidus and the solidus temperature, and wherein the lightweight alloy comprises the lightweight metal and one or more alloying elements, the method comprises the steps of:
 providing at least one starting composition for producing the lightweight alloy, including at least one lightweight metal based composition which comprises predominantly the lightweight metal;   producing the lightweight alloy in a form of a melt from the at least one starting composition;   ejecting the lightweight alloy melt from at least one nozzle; and   rapidly solidifying the lightweight alloy melt exiting the at least one nozzle thereby producing the solidified lightweight alloy, the lightweight alloy melt exiting the at least one nozzle having a predetermined temperature upon exiting the at least one nozzle and being cooled down within a predetermined period of time to the solidus temperature of the lightweight alloy at an average cooling rate which is determined as a ratio of the difference between the predetermined temperature and the solidus temperature over the predetermined period of time and which is in particular higher than 10,000° C./sec,   wherein   the lightweight metal based composition is heated, in a first heating step, to a first temperature which is lower than the liquidus temperature to produce a melt of the lightweight metal based composition having the first temperature, which lightweight metal based composition melt is supplied through a piping to the at least one nozzle; and   the lightweight alloy melt, which comprises at least the lightweight metal based composition melt, is heated in the piping to have a second temperature before being ejected from the at least one nozzle, which second temperature is higher than the first temperature and is at least 75% of the liquidus/solidus temperature difference higher than the solidus temperature.   
     
     
         2 . The method according to  claim 1 , wherein the second temperature is equal to or higher than the liquidus temperature, preferably at least 10° C. and more preferably at least 20° C. higher than the liquidus temperature. 
     
     
         3 . The method according to  claim 1 , wherein the predetermined temperature is equal to or higher than the liquidus temperature, preferably at least 10° C. and more preferably at least 20° C. higher than the liquidus temperature. 
     
     
         4 . The method according to  claim 1 , wherein the lightweight alloy melt has a residence time of at least 10 seconds, preferably at least 15 seconds and more preferably at least 20 seconds in the piping. 
     
     
         5 . The method according to  claim 1 , wherein the lightweight alloy is an aluminium alloy and the one or more alloying elements comprise one or more elements forming dispersoids in the aluminium alloy, the elements being transition metals, in particular transition metals selected from the group consisting of manganese (Mn), chromium (Cr), vanadium (V), titanium (Ti), zirconium (Zr), molybdenum (Mo), cobalt (Co), niobium (Nb), scandium (Sc), hafnium (Hf), nickel (Ni), yttrium (Y) and iron (Fe). 
     
     
         6 . The method according to  claim 5 , wherein the one or more alloying elements comprise chromium (Cr), vanadium (V), titanium (Ti), zirconium (Zr), molybdenum (Mo), cobalt (Co) and/or niobium (Nb), the total amount of Cr, V, Ti, Zr, Mo, Co and Nb being preferably at least equal to 0.50 wt. %, more preferably at least equal to 0.70 wt. % and most preferably at least equal to 1.00 wt. % of the aluminium alloy and the maximum amounts of these alloying elements being preferably 1.50 wt. % for Cr, 1.50 wt. % for V, 1.00 wt. % for Ti, 1.00 wt. % for Zr, 1.50 wt. % for Mo, 1.50 wt. % for Co and 1.00 wt. % for Nb. 
     
     
         7 . The method according to  claim 5 , wherein the one or more alloying elements comprise one or more elements forming a solid solution in the aluminium alloy, which solid solution forming elements comprise copper, zinc, magnesium and/or manganese, the aluminium alloy preferably comprising between 3.00 and 10.00 wt. % of magnesium (Mg) and more than 1.00 but less than 6.00 wt. % of manganese. 
     
     
         8 . The method according to  claim 1 , wherein the lightweight alloy is a magnesium alloy and the one or more alloying elements comprise silicon (Si), germanium (Ge), zirconium (Zr) and/or cobalt (Co). 
     
     
         9 . The method according to  claim 1 , wherein at least one of the alloying elements is present in the lightweight alloy in an amount higher than a solubility of the element at the solidus temperature in the lightweight alloy. 
     
     
         10 . The method according to  claim 1 , wherein the liquidus temperature is at least 25° C., in particular at least 50° C. and more particularly at least 75° C. or at least 100° C. higher than the solidus temperature. 
     
     
         11 . The method according to  claim 1 , wherein the first temperature is lower than 750° C., preferably lower than 725° C. and more preferably lower than 700° C. 
     
     
         12 . The method according to  claim 1 , wherein the first temperature is at least 10° C., in particular at least 20° C. and more particularly at least 30° C. lower than the liquidus temperature. 
     
     
         13 . The method according to  claim 1 , wherein the lightweight metal based composition melt is urged, by pipe flow, through the piping to the at least one nozzle. 
     
     
         14 . The method according to  claim 1 , wherein the lightweight metal based composition melt is degassed before being supplied through the piping to the at least one nozzle. 
     
     
         15 . The method according to  claim 1 , wherein the piping comprises at least one heating chamber for further heating the lightweight alloy melt. 
     
     
         16 . The method according to  claim 1 , wherein the lightweight metal based composition is only partially molten to produce the lightweight metal based composition melt by heating it to the first temperature and is further molten by heating it to the higher temperature in the piping. 
     
     
         17 . The method according to  claim 16 , characterised in wherein the lightweight alloy is produced from one starting composition, which starting composition is only partially molten by heating it to the first temperature to produce the lightweight metal based composition melt forming the lightweight alloy melt, which lightweight alloy melt is further molten in the piping by heating it to the second temperature in the piping. 
     
     
         18 . The method according to  claim 1 , wherein the lightweight alloy is produced from at least two starting compositions including the at least one lightweight metal based composition and at least one further composition, which further composition is added in the piping to the lightweight metal based composition melt to produce the lightweight alloy melt. 
     
     
         19 . The method according to  claim 18 , characterised in wherein the further composition is added to the lightweight metal based composition melt in a solid form. 
     
     
         20 . The method according to  claim 18 , characterised in wherein the further composition is added to the lightweight metal based composition melt in a liquid form. 
     
     
         21 . The method according to  claim 1 , wherein the piping comprises a mixing device for mixing the lightweight alloy melt. 
     
     
         22 . The method according to  claim 1 , wherein the first heating step is carried out in a furnace which is in liquid connection via the piping to the at least one nozzle, the lightweight metal based composition melt being fed at the first temperature from the furnace to the piping. 
     
     
         23 . The method according to  claim 1 , wherein the solidified lightweight alloy is plastically consolidated by plastic deformation under pressure, in particular by being extruded with a cross section reduction λ of at least 3, preferably of at least 6, more preferably of at least 8 and most preferably of at least 10.