New heat treatment process doubles the strength of die cast parts

Tag : Heat Treatment Furnace

Initiated in 2003 by the Australian Commonwealth Scientific andIndustrial Research Organisation (CSIRO)’s ‘NationalResearch Flagships’ programme includes a Light MetalsFlagship programme which has developed a new heat treatment processthat supplies stronger die cast parts – including doubledmechanical strength, higher fatigue resistance and improved energyabsorption.
“Our heat treatment methods offer major improvements intensile mechanical properties and enhancement of a range of othermaterial properties for high pressure die casting (HPDC)components,” says metallurgist Roger Lumley of the LightMetals Flagship.
Components treated with the new process show no surface blisteringor dimensional changes, and fatigue resistance of aluminium HPDCcomponents heat-treated with the new process can be as high as forsome wrought aluminium products. The new procedures may alsosubstantially raise energy absorption during fracture, which hassignificant implications for crash-sensitive structural componentsmade by high-pressure die-casting. For example, one commonsecondary alloy almost doubles in energy absorption, whenheat-treated specifically for this purpose.
Treated parts exhibit thermal conductivity about 20% above theiras-cast status, so that for engine or transmission applicationsheat can be transferred or removed more efficiently and quickly.
Potentially, since heat extraction operates more effectively,heat-treated HPDC parts could operate with lower amounts of fluidin cooling and lubrications systems.
The researchers say the heat treatment process can easily beimplemented in existing manufacturing facilities using conventionalheat treatment equipment such as continuous belt furnaces,fluidised beds or furnace systems designed specifically for rapidheat treatment.
The researchers have also recently discovered a range of HPDCaluminium alloy compositions that display extraordinarily rapidstrengthening behaviour, which has major cost and energy usageimplications in manufacturing. These alloys can be heat treated tohigh strength levels during a total cycle time of 30 minutes anddevelop properties superior to conventional aluminium castingalloys requiring heat treatment in thermal cycles of up to 24hours.
HPDC is the most cost-effective process for making large quantitiesof complex aluminium components in near to final form. Typically,up to 20 small parts can be made per minute. Most are used invehicles, but the process is also important for other industries.
While other cast and wrought aluminium alloy parts can beheat-treated to improve their mechanical properties (such asstrength, hardness, toughness, fatigue and ductility), this has notbeen possible until now for high-pressure die-castings.
High-pressure die-castings contain trapped gas pores that expand,blister and distort the casting when heat treatment is applied.Previous attempts at making them heat-treatable have tried toremove porosity from the cast parts, but these proved costly andtime-consuming.
The new process may enable die-casters to make complex HPDCcomponents, such as engine blocks and transmission housings, usingup to 30% less alloy to achieve the same performance. Apart fromreducing manufacturing costs, the requirement for less metal willalso reduce vehicle weight, leading to lower fuel consumption andlower greenhouse gas emissions.