Study On Laser Remanufacturing Of Cast Iron

Cast iron is widely used in various kinds of equipment.Porosity and crack often appear in the surface or inside due to the working condition or the defects of the casting itself,coupled with the mistaken processing,which leads to the equipment failure.At present,the welding is the main method to repair cast iron,but the weldability of cast iron is poor and the defect of the welding area is easily appeared,such as porosity and crack.Laser cladding could solve the defects due to small heat affected zone compared with the welding.In this article,QT-400 and HT-250 are used as research subjects,and the porosity and crack of cast iron are studied during the laser remanufacturing process.Firstly,the mechanism of porosity was studied in detail during cast iron laser processing.The nodular cast iron and gray cast iron were remelted under the condition of argon shielding atmosphere and open atmosphere by using of fiber laser systems.The results show that the pores are not present in the molten pool of nodular cast iron,but the pores appeared in gray cast iron.Furthermore,the pores have different sources in the molten pool of gray cast iron: inner gas dissolving out and carbon-oxygen reaction.Especially,the pores only derive from the inner gas dissolving out under the condition of argon shielding atmosphere.Semiconductor laser systems were used to analyze the pores in cladding layer.Results indicates that the pores are CO gas which generated by the carbon-oxygen reaction during laser cladding L1 powder on nodular cast iron,while the inner gas dissolving out of gray cast iron is another way to generate pores except for carbon-oxygen reaction.Secondly,the basic laser cladding process was studied by using semiconductor laser systems.During single-track laser cladding L1 powder on QT-400,the effect of cladding process on the morphology of cladding layer was investigated.Results show that the dilution rate has an important effect on pores in the cladding layer.Simultaneously,the process of multi-track overlapping laser cladding was also studied,which laid the foundation for the subsequent process optimization.Finally,the QT-400 substrate that has pre-made groove was repaired depending on the process of multiple-layer laser cladding L1 powder on nodular cast iron according to the above research.There are no cracks in the repair zone and only a small amount of pores appeared near the bonding zone.The size of the pores is much smaller than that in the cast iron.The experiments show that it is feasible to repair the cast iron by means of laser remanufacturing.In this paper,the formation mechanism of the porosity is study for the first time during cast iron laser remelting and laser cladding,and the effect of laser processing on the cladding layer is also studied,which provides a certain theory for laser repairing of cast iron.In addition,there are still some problems that need to be studied in the next step in laser repairing of cast iron,such as hard phase of the repair layer and the complicated shape of repair zone.