Chemical additions to reduce hot tearing in the cast house

Hot tear susceptibility in VDC casting is strongly affected by the chemical additions of alloys, hardeners and grain refiners. This paper assesses a few different approaches to reducing hot tearing in the cast house. Grain refinement is one commonly used approach, including dosing at cast start. Another technique is to control the alloy content, through the additions of Si, Mg, Mn or Fe which can influence the type and amount of intermetallics present during the final stages of solidification when hot tearing occurs. This paper summarizes experimental findings which assess the influence of additions on a hot tear rating, particularly in 6xxx series alloys. Strategies which could be used in the cast house are discussed. While changes to the bulk metal can have consequences for alloy specification and quality control, additions at cast start could be used to reduce scrap from hot tearing without changing the composition of the saleable product.