No abstract

In Selective Laser Melting, the initial units produced are single tracks that overlap to create a single layer; from the sequence of layers, a 3D object is manufactured. The properties of the parts produced by SLM depend heavily on the properties of each single track and each layer formed by these tracks. This study evaluates the effect of processing parameters on the geometrical characteristics of single tracks manufactured from 17-4PH stainless steel powder. A single-mode continuous-wave ytterbium fibre laser was used to manufacture single tracks at laser powers in the range of 100-300 W with a constant spot size of ∼80µm. The single tracks produced were subjected to standard metallographic preparation techniques for further analysis with an optical microscope. Deep molten pool shapes were observed at low scan speeds, while shallow molten pool shapes were observed at high scan speeds. At higher laser power densities, under-cutting and humping effects were also observed. The dimensions of single tracks processed without powder generally decrease with increasing scan speed at constant laser power. However, the geometrical features of the single tracks processed with powder revealed pronounced irregularities believed to be caused by non-homogeneity in the deposited powder layer. OPSOMMINGSelektiewe lasersmelting produseer enkel bane wat mekaar oordek en vorm so ʼn enkele laag. Daaropvolgende lae vorm dan ʼn driedimensionele onderdeel. Die eienskappe van hierdie onderdele word grootliks beïnvloed deur die eienskappe van elke baan en elke laag. Hierdie studie evalueer die effek van die prosesseringsparameters op die geometriese eienskappe van enkel bane wat van 17-4PH vlekvrye staalpoeier vervaardig is. ʼn Enkelmodus kontinuegolf ytterbium vesel laser is gebruik om die enkel bane te vervaardig. Die laser drywing het gewissel van 100 tot 300W met ʼn konstante kolgrootte van ongeveer 80µm. Die enkel bane is dan aan standaard metallografiese voorbereidingstegnieke onderwerp sodat verdere analise met ʼn optiese mikroskoop kon geskied. Diepgesmelte poel vorms is bespeur teen lae skandeersnelhede, terwyl vlakgesmelte poel vorms by hoë skandeersnelhede gewaar is. By hoër laser drywingsdigthede is ondersnyding en hobbelvorming waargeneem. Die dimensies van die enkel bane wat sonder poeier geprosesseer is, het oor die algemeen afgeneem met ʼn toename in skandeersnelheid by konstante laserdrywing. Die geometriese eienskappe van die enkel bane wat wel met poeier geprosesseer is, het noemenswaardige onreëlmatighede aan die lig gebring. Daar word vermoed dat die onreëlmatighede as gevolg van nie-homogene verskynsels in die gedeponeerde poeierlaag is.

No abstract

Samples of aluminium alloy A356 were manufactured by Semi Solid Metals HPDC technology, developed recently in CSIR-Pretoria. They were butt welded in as cast conditions using an Nd:YAG laser. The base metal and weld microstructure were presented. The effect of different heat treatments on microstructure and mechanical properties of the welds were investigated. It was found that the fine dendrite structure of the weld metal contributed for equalizing the mechanical properties of the joint.

CSIR-Rheo technology process which involves the preparation of metal slurry direct from liquid alloys by stirring and cooling was applied for treatment of Al-7%Si-0.35%Mg alloy, A356, to the Semi-Solid Metal state. Plates were cast in steel moulds with a 50 Ton High Pressure Die Casting machine. Heat treatments T4 and T6 were given to the samples. Butt laser welding was performed on the heat treated and as fabricated plates (F). Tensile properties, hardness profile, microstructure of the weld, heat affected zone and base metal were examined. Some comments on outcomes of the research are included.