Spray forming,which is the alloy with high-pressure inert gas flow atomized into small drop, flying under the high speed air flow and cooling,and deposited into the blank pieces before completed= solidification. It has the advantages of fine grain size, uniform and isostropic, can inhibit various advantages of rapid solidification technology such as macro segregation, but also has the advantages from the alloy molten to near net shape, thus, has caused the great attention.
Aluminum alloy has the properties of low density, high strength, good toughness and corrosion resistance and other advantages, is widely used as structural materials in the aerospace industry, at the same time, also are actively developing as automobile advanced materials and applied to high-level car engine.
Casting process is the main preparation method of traditional aluminum alloys, however, it has been difficult to meet the requirements for high-performance aluminum alloys.Firstly,the conventional process have been difficult to further improve strength,ductility, stiffness, heat resistance and corrosion resistance;Secondly, in the process of high-performance,the casting process cost increased rapidly thanks to the added equipments and decline of yield.Thirdly,as the alloy content rise,the ductility often decreases,so the subsequent pressure processing cost increases and bring down the finished products rate.Therefore, the high cost of production has greatly raised the use threshold of advanced aluminum alloy, also seriously affecting the development of the overall market scale.Among these aspects, the spray forming technolgoy has the advantages of excellent performance and comprehensive cost,can reduce the use of advanced aluminum alloys,further improve the comprehensive properties,to acheive the replacement steel with aluminum alloys in a certain range,thus, rapidly cultivating advanced aluminum alloy market, in turn, promotes the spray forming process to obtain cost superiority.
Nowadays,the successfully spray forming of high performance aluminum alloys mainly have the following aspects:
■High strength aluminum alloys.For example,Al-Zn ultra high strength aluminum alloys.Since the wide range of solidified crystallization and difference of specific gravity of Al-Zn alloys, when it is produced by a conventional casting method, macro-segregation tends to occur and big thermal cracking tendency.The rapid solidification characteristic of spray forming technology can solve these problems. It has been used in aerospace avionic parts and key parts of connecting rod and shaft support seat of automobile engine.
■High specific strength,high specific modulus of aluminum alloys.Al-Li alloys have the features of low density and high elastic modulus,and are a structural materials for aviation and aerospace with development protential.To a certain extent,ingot metallurgy processing limits the protential performance of Al-Li alloy.While,spray formed rapid solidification technology opens up a new way for the development of Al-Li alloy.
■Low expansion,high wear-resistance aluminum alloys.For example,high strength and wear-resistance for hypereutectic Al-Si alloys.The alloy has the advantages of low thermal expansion coefficient(CTE) and good abrasion resistance, etc.However,when the conventional casting process is adopted,will form the massive primary silicon and suffer the deterioration of material properties.The rapid solidification characteristics of spray forming effectively overcome this problem. At present,the spray forming Al-Si alloy has been made into car engine cylinder liners and other parts in developed countries.
■Heat resistance aluminum alloys.For example,Al-Fe-V-Si series heat resistance alloys.These alloys have the key performance of good room temperature, strength and toughness at high temperature,excellent corrosion resistance,it can be used in the range of 150℃~300℃,or even at a higher temperature,partly substitute work in the temperature range of titanium alloy and heat resistant steel, so as to reduce the weight and cost.The spray forming process can directly produce the billets with the characteristics of rapid solidification structure, overall compactness and large size from the liquid metal through fewer processes, in order to solve the problems of the traditional process.
■Aluminum matrix composites.A ‘sprayco-deposition’ technique was developed by combining the spray forming process with the preparationtechnology of aluminum matrix composite materials.