Study On The Protection Agent In Fusion Welding Between Aluminum And Steel

A special protection agent was developed for aluminum-steel fusion welding in this dissertation,Basing on the difficulty of fusion welding between aluminum and steel and current level of welding between aluminum and steel.Using Vacuum furnace, simultaneous thermal analyzer (DCS-TGA), X-ray diffraction (XRD) to compare the spreading ablity of the protection agent, to find melting point and the components of the protection agent, using high-frequency induction to realize the fusion welding between aluminum and steel.Using SANS testing machine, hardness tester to determin the mechanical properties of joints.using optical microscopy, scanning electron microscopy (SEM) to analyse the joint interface organization and the composition.The result of vacuum furnace spreading test for protection agent for show that the sample 13,sample 9,sample 11 has the best of the spreadability, spreading area are 790.8mm2, 720mm2,650.4mm2. While the sample 14 has the smallest spread aera 14.365mm2.It is OK for the melting point of protection agent for Aluminum-steel fursion welding is between 450 and 630℃.Using DCS-TGA experiments to determine the melting point, the results show that the sample 9 has a lowest melting point,488℃and the highest melting point of sample 13, reached 610℃, which is 1.25 times of the melting point of sample 9.Using X-ray diffraction analysis to determine composition of the protection agents, experimental results show that the sample 9 is constited by KAlF4, AlF3, K2AlF5, Cs2KAl3F12, KF, CsAlF4 There is a new phase AlCl3 in samples 11.In sample 13,there is two new phase AlCl3 and KCaF3.selected.protection agents which has a better spreading performance to do fursion welding experiments between aluminum and steel.The results of mechanical properties experiments show that the highest shear strength i value is 15MPa which used sample 13,and in hardness test, the hardness reach the largest value 612.9HVo.2 in the compound layer part. Use the reaction-scanning electron microscopy analyser to sure the main intermetal compound,there are Fe3Al, FeAl2Si, Al+τ5+FeAl3 some brittle intermetal phase in interface and its compounds thickness is 20um.The shear strength of welded joints which use sample 9 as protection agent is 14MPa. SEM photo show that the joint interface layer whose protective agent is sample 9 is divided into two layers, the compound thickness of steel side is 15um, mainly composed of Al+τ5+FeAl3, and there is some diffuse state compound distribution between aluminum side and metal parts compounds. The shear strength of welded joints which use sample 11 as protection agent is 8 MPa and the interface is consist of FeAl+α-Al,FeAl3 and Al0.72Fe0.18Si0.10.SEM electron micrographs showed there is residue in the aluminum-steel fursion welding Department.The sample 11 has maximum amount residues,and Continuous distribute in the aluminum-steel interface,keep separate between the aluminum atoms and iron atoms.The residue of sample 13 has block forming, separation distribution in steel side of aluminum-steel fusion welding joint. Sample 9 residues has dot forming and closely arranged distributed in the intermetallic compounds which formd the joint of aluminum-steel fursion welding. The forming and distribution of protection agents residue has much relation with their composition, sample 11 has KCl which has a floating effect,which lead protective agent residues in the float process with KCl,for the cooling speed, stay at aluminum side in the joint interface.